diff --git a/dotnet/samples/01-get-started/01_hello_agent/Program.cs b/dotnet/samples/01-get-started/01_hello_agent/Program.cs
index e461f9ba75..5e866f1d83 100644
--- a/dotnet/samples/01-get-started/01_hello_agent/Program.cs
+++ b/dotnet/samples/01-get-started/01_hello_agent/Program.cs
@@ -8,7 +8,7 @@ using Microsoft.Agents.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/01-get-started/02_add_tools/Program.cs b/dotnet/samples/01-get-started/02_add_tools/Program.cs
index da0b638562..e43f366c68 100644
--- a/dotnet/samples/01-get-started/02_add_tools/Program.cs
+++ b/dotnet/samples/01-get-started/02_add_tools/Program.cs
@@ -11,7 +11,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 [Description("Get the weather for a given location.")]
 static string GetWeather([Description("The location to get the weather for.")] string location)
diff --git a/dotnet/samples/01-get-started/03_multi_turn/Program.cs b/dotnet/samples/01-get-started/03_multi_turn/Program.cs
index 5d49e806ed..1887a22b4f 100644
--- a/dotnet/samples/01-get-started/03_multi_turn/Program.cs
+++ b/dotnet/samples/01-get-started/03_multi_turn/Program.cs
@@ -8,7 +8,7 @@ using Microsoft.Agents.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/01-get-started/04_memory/Program.cs b/dotnet/samples/01-get-started/04_memory/Program.cs
index a97941620f..ebafc60b45 100644
--- a/dotnet/samples/01-get-started/04_memory/Program.cs
+++ b/dotnet/samples/01-get-started/04_memory/Program.cs
@@ -16,7 +16,7 @@ using OpenAI.Chat;
 using SampleApp;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/01-get-started/06_host_your_agent/Program.cs b/dotnet/samples/01-get-started/06_host_your_agent/Program.cs
index 6012119b25..c106f2e4f2 100644
--- a/dotnet/samples/01-get-started/06_host_your_agent/Program.cs
+++ b/dotnet/samples/01-get-started/06_host_your_agent/Program.cs
@@ -8,7 +8,7 @@
 //
 // Environment variables:
 //   AZURE_OPENAI_ENDPOINT
-//   AZURE_OPENAI_DEPLOYMENT_NAME (defaults to "gpt-4o-mini")
+//   AZURE_OPENAI_DEPLOYMENT_NAME (defaults to "gpt-5.4-mini")
 //
 // Run with: func start
 // Then call: POST http://localhost:7071/api/agents/HostedAgent/run
@@ -23,7 +23,7 @@ using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT")
     ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Set up an AI agent following the standard Microsoft Agent Framework pattern.
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/AGUI/README.md b/dotnet/samples/02-agents/AGUI/README.md
index f55e317e36..77a58b3198 100644
--- a/dotnet/samples/02-agents/AGUI/README.md
+++ b/dotnet/samples/02-agents/AGUI/README.md
@@ -15,7 +15,7 @@ All samples require the following environment variables:
 
 ```bash
 export AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/"
-export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 For the client samples, you can optionally set:
diff --git a/dotnet/samples/02-agents/AgentOpenTelemetry/Program.cs b/dotnet/samples/02-agents/AgentOpenTelemetry/Program.cs
index 83445dc1fc..d1cd5a50c9 100644
--- a/dotnet/samples/02-agents/AgentOpenTelemetry/Program.cs
+++ b/dotnet/samples/02-agents/AgentOpenTelemetry/Program.cs
@@ -97,7 +97,7 @@ Console.WriteLine("""
     """);
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT environment variable is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Log application startup
 appLogger.LogInformation("OpenTelemetry Aspire Demo application started");
diff --git a/dotnet/samples/02-agents/AgentOpenTelemetry/README.md b/dotnet/samples/02-agents/AgentOpenTelemetry/README.md
index 229d37dca6..d79c00eb87 100644
--- a/dotnet/samples/02-agents/AgentOpenTelemetry/README.md
+++ b/dotnet/samples/02-agents/AgentOpenTelemetry/README.md
@@ -34,7 +34,7 @@ graph TD
 Set the following environment variables:
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/"
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
 
 **Note**: This demo uses Azure CLI credentials for authentication. Make sure you're logged in with `az login` and have access to the Azure OpenAI resource.
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIAgentsPersistent/Program.cs b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIAgentsPersistent/Program.cs
index a4b702be2c..af41e69c77 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIAgentsPersistent/Program.cs
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIAgentsPersistent/Program.cs
@@ -9,7 +9,7 @@ using Azure.Identity;
 using Microsoft.Agents.AI;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 const string JokerName = "Joker";
 const string JokerInstructions = "You are good at telling jokes.";
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIAgentsPersistent/README.md b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIAgentsPersistent/README.md
index 7c92d809d3..dbe7c2c12f 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIAgentsPersistent/README.md
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIAgentsPersistent/README.md
@@ -22,5 +22,5 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project" # Replace with your Microsoft Foundry resource endpoint
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIProject/Program.cs b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIProject/Program.cs
index f5321c4350..233705d4af 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIProject/Program.cs
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIProject/Program.cs
@@ -9,7 +9,7 @@ using Microsoft.Agents.AI;
 using Microsoft.Agents.AI.Foundry;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 const string JokerName = "JokerAgent";
 
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIProject/README.md b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIProject/README.md
index ec688df59d..0e225751fb 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIProject/README.md
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureAIProject/README.md
@@ -22,5 +22,5 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project" # Replace with your Microsoft Foundry resource endpoint
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIChatCompletion/Program.cs b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIChatCompletion/Program.cs
index 1f83f6fbef..024adf626d 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIChatCompletion/Program.cs
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIChatCompletion/Program.cs
@@ -8,7 +8,7 @@ using Microsoft.Agents.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIChatCompletion/README.md b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIChatCompletion/README.md
index 4cacf30131..2c22cd623e 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIChatCompletion/README.md
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIChatCompletion/README.md
@@ -12,5 +12,5 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIResponses/Program.cs b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIResponses/Program.cs
index f29b850700..279cadc12b 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIResponses/Program.cs
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIResponses/Program.cs
@@ -9,7 +9,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Responses;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIResponses/README.md b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIResponses/README.md
index 4cacf30131..2c22cd623e 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIResponses/README.md
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_AzureOpenAIResponses/README.md
@@ -12,5 +12,5 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIChatCompletion/Program.cs b/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIChatCompletion/Program.cs
index f5af4d2369..3d7ed3a871 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIChatCompletion/Program.cs
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIChatCompletion/Program.cs
@@ -8,7 +8,7 @@ using OpenAI;
 using OpenAI.Chat;
 
 var apiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY") ?? throw new InvalidOperationException("OPENAI_API_KEY is not set.");
-var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-4o-mini";
+var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-5.4-mini";
 
 AIAgent agent = new OpenAIClient(
     apiKey)
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIChatCompletion/README.md b/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIChatCompletion/README.md
index ef7ce3ae02..3f61854aa6 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIChatCompletion/README.md
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIChatCompletion/README.md
@@ -9,5 +9,5 @@ Set the following environment variables:
 
 ```powershell
 $env:OPENAI_API_KEY="*****" # Replace with your OpenAI api key
-$env:OPENAI_CHAT_MODEL_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:OPENAI_CHAT_MODEL_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIResponses/Program.cs b/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIResponses/Program.cs
index baa6677a4f..456aaafef0 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIResponses/Program.cs
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIResponses/Program.cs
@@ -7,7 +7,7 @@ using OpenAI;
 using OpenAI.Responses;
 
 var apiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY") ?? throw new InvalidOperationException("OPENAI_API_KEY is not set.");
-var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-4o-mini";
+var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-5.4-mini";
 
 AIAgent agent = new OpenAIClient(
     apiKey)
diff --git a/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIResponses/README.md b/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIResponses/README.md
index ef7ce3ae02..3f61854aa6 100644
--- a/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIResponses/README.md
+++ b/dotnet/samples/02-agents/AgentProviders/Agent_With_OpenAIResponses/README.md
@@ -9,5 +9,5 @@ Set the following environment variables:
 
 ```powershell
 $env:OPENAI_API_KEY="*****" # Replace with your OpenAI api key
-$env:OPENAI_CHAT_MODEL_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:OPENAI_CHAT_MODEL_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/Program.cs b/dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/Program.cs
index b787bb86a3..f6b9b58b79 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/Program.cs
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/Program.cs
@@ -16,7 +16,7 @@ using OpenAI.Responses;
 
 // --- Configuration ---
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // --- Skills Provider ---
 // Discovers skills from the 'skills' directory containing SKILL.md files.
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/README.md b/dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/README.md
index 592aca4a27..0c5b7f8416 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/README.md
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step01_FileBasedSkills/README.md
@@ -30,7 +30,7 @@ Converts between common units (miles↔km, pounds↔kg) using a multiplication f
 
 ```bash
 export AZURE_OPENAI_ENDPOINT="https://your-endpoint.openai.azure.com/"
-export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ### Run
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step02_CodeDefinedSkills/Program.cs b/dotnet/samples/02-agents/AgentSkills/Agent_Step02_CodeDefinedSkills/Program.cs
index 46c58985fb..8c1cfa33bb 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step02_CodeDefinedSkills/Program.cs
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step02_CodeDefinedSkills/Program.cs
@@ -16,7 +16,7 @@ using OpenAI.Responses;
 
 // --- Configuration ---
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // --- Build the code-defined skill ---
 var unitConverterSkill = new AgentInlineSkill(
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step02_CodeDefinedSkills/README.md b/dotnet/samples/02-agents/AgentSkills/Agent_Step02_CodeDefinedSkills/README.md
index 5b7c8747dd..bb31b25713 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step02_CodeDefinedSkills/README.md
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step02_CodeDefinedSkills/README.md
@@ -31,7 +31,7 @@ Converts between common units using multiplication factors. Defined entirely in
 
 ```bash
 export AZURE_OPENAI_ENDPOINT="https://your-endpoint.openai.azure.com/"
-export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ### Run
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/Program.cs b/dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/Program.cs
index fb0f202230..8be991598a 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/Program.cs
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/Program.cs
@@ -11,7 +11,7 @@ using OpenAI.Responses;
 
 // --- Configuration ---
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // --- Class-Based Skill ---
 // Instantiate the skill class.
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/README.md b/dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/README.md
index 506784256a..3525bb7a98 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/README.md
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step03_ClassBasedSkills/README.md
@@ -28,7 +28,7 @@ A `UnitConverterSkill` class that converts between common units. Defined in `Pro
 
 ```bash
 export AZURE_OPENAI_ENDPOINT="https://your-endpoint.openai.azure.com/"
-export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ### Run
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/Program.cs b/dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/Program.cs
index b8a9e8fbb1..ab5da71a3c 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/Program.cs
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/Program.cs
@@ -22,7 +22,7 @@ using OpenAI.Responses;
 // --- Configuration ---
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT")
     ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // --- 1. Code-Defined Skill: volume-converter ---
 var volumeConverterSkill = new AgentInlineSkill(
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/README.md b/dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/README.md
index 14a0d089b9..7681359414 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/README.md
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step04_MixedSkills/README.md
@@ -45,7 +45,7 @@ Defined as `TemperatureConverterSkill` class in `Program.cs`. Converts °F↔°C
 
 ```bash
 export AZURE_OPENAI_ENDPOINT="https://your-endpoint.openai.azure.com/"
-export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+export AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ### Run
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step05_SkillsWithDI/Program.cs b/dotnet/samples/02-agents/AgentSkills/Agent_Step05_SkillsWithDI/Program.cs
index f0c5a4c8a5..50b0545be3 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step05_SkillsWithDI/Program.cs
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step05_SkillsWithDI/Program.cs
@@ -22,7 +22,7 @@ using OpenAI.Responses;
 
 // --- Configuration ---
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // --- DI Container ---
 // Register application services that skill resources and scripts can resolve at execution time.
diff --git a/dotnet/samples/02-agents/AgentSkills/Agent_Step05_SkillsWithDI/README.md b/dotnet/samples/02-agents/AgentSkills/Agent_Step05_SkillsWithDI/README.md
index b284b745d5..296f90ef09 100644
--- a/dotnet/samples/02-agents/AgentSkills/Agent_Step05_SkillsWithDI/README.md
+++ b/dotnet/samples/02-agents/AgentSkills/Agent_Step05_SkillsWithDI/README.md
@@ -45,7 +45,7 @@ Set the following environment variables:
 | Variable | Description |
 |---|---|
 | `AZURE_OPENAI_ENDPOINT` | Your Azure OpenAI endpoint URL |
-| `AZURE_OPENAI_DEPLOYMENT_NAME` | Model deployment name (defaults to `gpt-4o-mini`) |
+| `AZURE_OPENAI_DEPLOYMENT_NAME` | Model deployment name (defaults to `gpt-5.4-mini`) |
 
 ## Running the Sample
 
diff --git a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step01_ChatHistoryMemory/Program.cs b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step01_ChatHistoryMemory/Program.cs
index ff4628ef7a..46ef6807cd 100644
--- a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step01_ChatHistoryMemory/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step01_ChatHistoryMemory/Program.cs
@@ -12,7 +12,7 @@ using Microsoft.SemanticKernel.Connectors.InMemory;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var embeddingDeploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_EMBEDDING_DEPLOYMENT_NAME") ?? "text-embedding-3-large";
 
 // Create a vector store to store the chat messages in.
diff --git a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step02_MemoryUsingMem0/Program.cs b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step02_MemoryUsingMem0/Program.cs
index f1842eb634..c3a4fc291e 100644
--- a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step02_MemoryUsingMem0/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step02_MemoryUsingMem0/Program.cs
@@ -14,7 +14,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 var mem0ServiceUri = Environment.GetEnvironmentVariable("MEM0_ENDPOINT") ?? throw new InvalidOperationException("MEM0_ENDPOINT is not set.");
 var mem0ApiKey = Environment.GetEnvironmentVariable("MEM0_API_KEY") ?? throw new InvalidOperationException("MEM0_API_KEY is not set.");
diff --git a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step04_MemoryUsingFoundry/Program.cs b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step04_MemoryUsingFoundry/Program.cs
index 1132e9ef1d..402ae47a2d 100644
--- a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step04_MemoryUsingFoundry/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step04_MemoryUsingFoundry/Program.cs
@@ -15,7 +15,7 @@ using Microsoft.Agents.AI.Foundry;
 
 string foundryEndpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
 string memoryStoreName = Environment.GetEnvironmentVariable("AZURE_AI_MEMORY_STORE_ID") ?? "memory-store-sample";
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 string embeddingModelName = Environment.GetEnvironmentVariable("AZURE_AI_EMBEDDING_DEPLOYMENT_NAME") ?? "text-embedding-ada-002";
 
 // Create an AIProjectClient for Foundry with Azure Identity authentication.
diff --git a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step04_MemoryUsingFoundry/README.md b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step04_MemoryUsingFoundry/README.md
index b2d52e9837..e863b2eada 100644
--- a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step04_MemoryUsingFoundry/README.md
+++ b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step04_MemoryUsingFoundry/README.md
@@ -14,7 +14,7 @@ This sample demonstrates how to create and run an agent that uses Microsoft Foun
 ## Prerequisites
 
 1. Azure subscription with Microsoft Foundry project
-2. Azure OpenAI resource with a chat model deployment (e.g., gpt-4o-mini) and an embedding model deployment (e.g., text-embedding-ada-002)
+2. Azure OpenAI resource with a chat model deployment (e.g., gpt-5.4-mini) and an embedding model deployment (e.g., text-embedding-ada-002)
 3. .NET 10.0 SDK
 4. Azure CLI logged in (`az login`)
 
@@ -26,7 +26,7 @@ export AZURE_AI_PROJECT_ENDPOINT="https://your-account.services.ai.azure.com/api
 export AZURE_AI_MEMORY_STORE_ID="my_memory_store"
 
 # Model deployment names (models deployed in your Foundry project)
-export AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+export AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 export AZURE_AI_EMBEDDING_DEPLOYMENT_NAME="text-embedding-ada-002"
 ```
 
diff --git a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step05_BoundedChatHistory/Program.cs b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step05_BoundedChatHistory/Program.cs
index ab3a0376eb..053fabb7bb 100644
--- a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step05_BoundedChatHistory/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step05_BoundedChatHistory/Program.cs
@@ -15,7 +15,7 @@ using OpenAI.Chat;
 using SampleApp;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var embeddingDeploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_EMBEDDING_DEPLOYMENT_NAME") ?? "text-embedding-3-large";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step05_BoundedChatHistory/README.md b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step05_BoundedChatHistory/README.md
index c1e35f5a88..4d6f88ce51 100644
--- a/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step05_BoundedChatHistory/README.md
+++ b/dotnet/samples/02-agents/AgentWithMemory/AgentWithMemory_Step05_BoundedChatHistory/README.md
@@ -13,7 +13,7 @@ This sample demonstrates how to create a custom `ChatHistoryProvider` that keeps
 
 - [.NET 10 SDK](https://dotnet.microsoft.com/download/dotnet/10.0)
 - An Azure OpenAI resource with:
-  - A chat deployment (e.g., `gpt-4o-mini`)
+  - A chat deployment (e.g., `gpt-5.4-mini`)
   - An embedding deployment (e.g., `text-embedding-3-large`)
 
 ## Configuration
@@ -23,7 +23,7 @@ Set the following environment variables:
 | Variable | Description | Default |
 |---|---|---|
 | `AZURE_OPENAI_ENDPOINT` | Your Azure OpenAI endpoint URL | *(required)* |
-| `AZURE_OPENAI_DEPLOYMENT_NAME` | Chat model deployment name | `gpt-4o-mini` |
+| `AZURE_OPENAI_DEPLOYMENT_NAME` | Chat model deployment name | `gpt-5.4-mini` |
 | `AZURE_OPENAI_EMBEDDING_DEPLOYMENT_NAME` | Embedding model deployment name | `text-embedding-3-large` |
 
 ## Running the Sample
diff --git a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step01_Running/Program.cs b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step01_Running/Program.cs
index e82f420105..1b44ac3a54 100644
--- a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step01_Running/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step01_Running/Program.cs
@@ -7,7 +7,7 @@ using Microsoft.Agents.AI;
 using OpenAI.Responses;
 
 var apiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY") ?? throw new InvalidOperationException("OPENAI_API_KEY is not set.");
-var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-4o-mini";
+var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-5.4-mini";
 
 AIAgent agent =
     new ResponsesClient(new ApiKeyCredential(apiKey))
diff --git a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step02_Reasoning/Program.cs b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step02_Reasoning/Program.cs
index 12e30dc203..4fafbdf2b5 100644
--- a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step02_Reasoning/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step02_Reasoning/Program.cs
@@ -7,7 +7,7 @@ using Microsoft.Extensions.AI;
 using OpenAI;
 
 var apiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY") ?? throw new InvalidOperationException("OPENAI_API_KEY is not set.");
-var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-5";
+var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-5.4-mini";
 
 var client = new OpenAIClient(apiKey)
         .GetResponsesClient()
diff --git a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step03_CreateFromChatClient/Program.cs b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step03_CreateFromChatClient/Program.cs
index 5efc6c0ad6..b1076de051 100644
--- a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step03_CreateFromChatClient/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step03_CreateFromChatClient/Program.cs
@@ -7,7 +7,7 @@ using OpenAI.Chat;
 using OpenAIChatClientSample;
 
 string apiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY") ?? throw new InvalidOperationException("OPENAI_API_KEY is not set.");
-string model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-4o-mini";
+string model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-5.4-mini";
 
 // Create a ChatClient directly from OpenAIClient
 ChatClient chatClient = new OpenAIClient(apiKey).GetChatClient(model);
diff --git a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step03_CreateFromChatClient/README.md b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step03_CreateFromChatClient/README.md
index 9c91e964eb..78b3b7e8a4 100644
--- a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step03_CreateFromChatClient/README.md
+++ b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step03_CreateFromChatClient/README.md
@@ -13,7 +13,7 @@ This sample demonstrates how to create an AI agent directly from an `OpenAI.Chat
 1. Set the required environment variables:
    ```bash
    set OPENAI_API_KEY=your_api_key_here
-   set OPENAI_CHAT_MODEL_NAME=gpt-4o-mini
+   set OPENAI_CHAT_MODEL_NAME=gpt-5.4-mini
    ```
 
 2. Run the sample:
diff --git a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step04_CreateFromOpenAIResponseClient/Program.cs b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step04_CreateFromOpenAIResponseClient/Program.cs
index dbd11ce3c6..7de38d2896 100644
--- a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step04_CreateFromOpenAIResponseClient/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step04_CreateFromOpenAIResponseClient/Program.cs
@@ -7,7 +7,7 @@ using OpenAI.Responses;
 using OpenAIResponseClientSample;
 
 var apiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY") ?? throw new InvalidOperationException("OPENAI_API_KEY is not set.");
-var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-4o-mini";
+var model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-5.4-mini";
 
 // Create a ResponsesClient directly from OpenAIClient
 ResponsesClient responseClient = new OpenAIClient(apiKey).GetResponsesClient();
diff --git a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step04_CreateFromOpenAIResponseClient/README.md b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step04_CreateFromOpenAIResponseClient/README.md
index 1acbe3137d..c0079ef5de 100644
--- a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step04_CreateFromOpenAIResponseClient/README.md
+++ b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step04_CreateFromOpenAIResponseClient/README.md
@@ -13,7 +13,7 @@ This sample demonstrates how to create an AI agent directly from an `OpenAI.Resp
 1. Set the required environment variables:
    ```bash
    set OPENAI_API_KEY=your_api_key_here
-   set OPENAI_CHAT_MODEL_NAME=gpt-4o-mini
+   set OPENAI_CHAT_MODEL_NAME=gpt-5.4-mini
    ```
 
 2. Run the sample:
diff --git a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step05_Conversation/Program.cs b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step05_Conversation/Program.cs
index a8dc73839a..407a03951e 100644
--- a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step05_Conversation/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step05_Conversation/Program.cs
@@ -15,7 +15,7 @@ using OpenAI.Chat;
 using OpenAI.Conversations;
 
 string apiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY") ?? throw new InvalidOperationException("OPENAI_API_KEY is not set.");
-string model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-4o-mini";
+string model = Environment.GetEnvironmentVariable("OPENAI_CHAT_MODEL_NAME") ?? "gpt-5.4-mini";
 
 // Create a ConversationClient directly from OpenAIClient
 OpenAIClient openAIClient = new(apiKey);
diff --git a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step05_Conversation/README.md b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step05_Conversation/README.md
index 1b4d393418..fa53974817 100644
--- a/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step05_Conversation/README.md
+++ b/dotnet/samples/02-agents/AgentWithOpenAI/Agent_OpenAI_Step05_Conversation/README.md
@@ -69,7 +69,7 @@ foreach (ClientResult result in getConversationItemsResults.GetRawPages())
 1. Set the required environment variables:
    ```powershell
    $env:OPENAI_API_KEY = "your_api_key_here"
-   $env:OPENAI_CHAT_MODEL_NAME = "gpt-4o-mini"
+   $env:OPENAI_CHAT_MODEL_NAME = "gpt-5.4-mini"
    ```
 
 2. Run the sample:
diff --git a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step01_BasicTextRAG/Program.cs b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step01_BasicTextRAG/Program.cs
index e1db6d3f4f..b20d6d31a6 100644
--- a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step01_BasicTextRAG/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step01_BasicTextRAG/Program.cs
@@ -15,7 +15,7 @@ using Microsoft.SemanticKernel.Connectors.InMemory;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var embeddingDeploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_EMBEDDING_DEPLOYMENT_NAME") ?? "text-embedding-3-large";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/Program.cs b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/Program.cs
index 2d6e30ae14..92de582569 100644
--- a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/Program.cs
@@ -14,7 +14,7 @@ using OpenAI.Chat;
 using Qdrant.Client;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var embeddingDeploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_EMBEDDING_DEPLOYMENT_NAME") ?? "text-embedding-3-large";
 var afOverviewUrl = "https://raw.githubusercontent.com/MicrosoftDocs/semantic-kernel-docs/refs/heads/main/agent-framework/overview/index.md";
 var afMigrationUrl = "https://raw.githubusercontent.com/MicrosoftDocs/semantic-kernel-docs/refs/heads/main/agent-framework/migration-guide/from-semantic-kernel/index.md";
diff --git a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/README.md b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/README.md
index ec69136e14..7875a5d3cf 100644
--- a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/README.md
+++ b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step02_CustomVectorStoreRAG/README.md
@@ -23,7 +23,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 $env:AZURE_OPENAI_EMBEDDING_DEPLOYMENT_NAME="text-embedding-3-large"  # Optional, defaults to text-embedding-3-large
 ```
 
diff --git a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step03_CustomRAGDataSource/Program.cs b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step03_CustomRAGDataSource/Program.cs
index d4e3a40756..2b7c28d345 100644
--- a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step03_CustomRAGDataSource/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step03_CustomRAGDataSource/Program.cs
@@ -13,7 +13,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 TextSearchProviderOptions textSearchOptions = new()
 {
diff --git a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step04_FoundryServiceRAG/Program.cs b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step04_FoundryServiceRAG/Program.cs
index c68310eae5..8fc21174a1 100644
--- a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step04_FoundryServiceRAG/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step04_FoundryServiceRAG/Program.cs
@@ -14,7 +14,7 @@ using OpenAI.Responses;
 using OpenAI.VectorStores;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create an AI Project client and get an OpenAI client that works with the foundry service.
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step05_Neo4jGraphRAG/Program.cs b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step05_Neo4jGraphRAG/Program.cs
index 5bf0918ab3..7e6b6942f6 100644
--- a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step05_Neo4jGraphRAG/Program.cs
+++ b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step05_Neo4jGraphRAG/Program.cs
@@ -8,7 +8,7 @@ using Neo4j.AgentFramework.GraphRAG;
 using Neo4j.Driver;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var neo4jUri = Environment.GetEnvironmentVariable("NEO4J_URI") ?? throw new InvalidOperationException("NEO4J_URI is not set.");
 var neo4jUsername = Environment.GetEnvironmentVariable("NEO4J_USERNAME") ?? "neo4j";
 var neo4jPassword = Environment.GetEnvironmentVariable("NEO4J_PASSWORD") ?? throw new InvalidOperationException("NEO4J_PASSWORD is not set.");
diff --git a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step05_Neo4jGraphRAG/README.md b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step05_Neo4jGraphRAG/README.md
index 418407e831..7295f89ca1 100644
--- a/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step05_Neo4jGraphRAG/README.md
+++ b/dotnet/samples/02-agents/AgentWithRAG/AgentWithRAG_Step05_Neo4jGraphRAG/README.md
@@ -15,7 +15,7 @@ The sample uses a Neo4j fulltext index for retrieval and a Cypher `RetrievalQuer
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/"
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 $env:NEO4J_URI="neo4j+s://your-instance.databases.neo4j.io"
 $env:NEO4J_USERNAME="neo4j"
 $env:NEO4J_PASSWORD="your-password"
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step01_UsingFunctionToolsWithApprovals/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step01_UsingFunctionToolsWithApprovals/Program.cs
index 8ff4181a51..ea3a3ccddd 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step01_UsingFunctionToolsWithApprovals/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step01_UsingFunctionToolsWithApprovals/Program.cs
@@ -14,7 +14,7 @@ using OpenAI.Chat;
 using ChatMessage = Microsoft.Extensions.AI.ChatMessage;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create a sample function tool that the agent can use.
 [Description("Get the weather for a given location.")]
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step02_StructuredOutput/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step02_StructuredOutput/Program.cs
index 7e74315e7d..3acb1bc125 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step02_StructuredOutput/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step02_StructuredOutput/Program.cs
@@ -14,7 +14,7 @@ using SampleApp;
 using ChatMessage = Microsoft.Extensions.AI.ChatMessage;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create chat client to be used by chat client agents.
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step02_StructuredOutput/README.md b/dotnet/samples/02-agents/Agents/Agent_Step02_StructuredOutput/README.md
index 9b9411f17e..babe679ea2 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step02_StructuredOutput/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step02_StructuredOutput/README.md
@@ -28,7 +28,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step03_PersistedConversations/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step03_PersistedConversations/Program.cs
index d3331cb2b8..d9404723f3 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step03_PersistedConversations/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step03_PersistedConversations/Program.cs
@@ -11,7 +11,7 @@ using Microsoft.Agents.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create the agent
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step04_3rdPartyChatHistoryStorage/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step04_3rdPartyChatHistoryStorage/Program.cs
index 78a8952082..ce0dfac645 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step04_3rdPartyChatHistoryStorage/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step04_3rdPartyChatHistoryStorage/Program.cs
@@ -18,7 +18,7 @@ using SampleApp;
 using ChatMessage = Microsoft.Extensions.AI.ChatMessage;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create a vector store to store the chat messages in.
 // Replace this with a vector store implementation of your choice if you want to persist the chat history to disk.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step05_Observability/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step05_Observability/Program.cs
index 20a0c252a2..3e7d7e6bd4 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step05_Observability/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step05_Observability/Program.cs
@@ -11,7 +11,7 @@ using OpenTelemetry;
 using OpenTelemetry.Trace;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var applicationInsightsConnectionString = Environment.GetEnvironmentVariable("APPLICATIONINSIGHTS_CONNECTION_STRING");
 
 // Create TracerProvider with console exporter
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step06_DependencyInjection/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step06_DependencyInjection/Program.cs
index 218ab1a10e..9e712d7a73 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step06_DependencyInjection/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step06_DependencyInjection/Program.cs
@@ -12,7 +12,7 @@ using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create a host builder that we will register services with and then run.
 HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step07_AsMcpTool/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step07_AsMcpTool/Program.cs
index 5ab4406abd..82b9e16fdd 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step07_AsMcpTool/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step07_AsMcpTool/Program.cs
@@ -11,7 +11,7 @@ using Microsoft.Extensions.Hosting;
 using ModelContextProtocol.Server;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step07_AsMcpTool/README.md b/dotnet/samples/02-agents/Agents/Agent_Step07_AsMcpTool/README.md
index 2feaee22e2..14b0835151 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step07_AsMcpTool/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step07_AsMcpTool/README.md
@@ -22,7 +22,7 @@ To use the [MCP Inspector](https://modelcontextprotocol.io/docs/tools/inspector)
 1. Open a web browser and navigate to the URL displayed in the terminal. If not opened automatically, this will open the MCP Inspector interface.
 1. In the MCP Inspector interface, add the following environment variables to allow your MCP server to access Microsoft Foundry Project to create and run the agent:
     - AZURE_AI_PROJECT_ENDPOINT = https://your-resource.openai.azure.com/ # Replace with your Microsoft Foundry Project endpoint
-    - AZURE_AI_MODEL_DEPLOYMENT_NAME = gpt-4o-mini # Replace with your model deployment name
+    - AZURE_AI_MODEL_DEPLOYMENT_NAME = gpt-5.4-mini # Replace with your model deployment name
 1. Find and click the `Connect` button in the MCP Inspector interface to connect to the MCP server.
 1. As soon as the connection is established, open the `Tools` tab in the MCP Inspector interface and select the `Joker` tool from the list.
 1. Specify your prompt as a value for the `query` argument, for example: `Tell me a joke about a pirate` and click the `Run Tool` button to run the tool.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step08_UsingImages/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step08_UsingImages/Program.cs
index 08e5b63139..fda3e872cc 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step08_UsingImages/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step08_UsingImages/Program.cs
@@ -9,7 +9,7 @@ using OpenAI.Chat;
 using ChatMessage = Microsoft.Extensions.AI.ChatMessage;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = System.Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o";
+var deploymentName = System.Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step08_UsingImages/README.md b/dotnet/samples/02-agents/Agents/Agent_Step08_UsingImages/README.md
index e70c09f513..ade4491942 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step08_UsingImages/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step08_UsingImages/README.md
@@ -20,7 +20,7 @@ This sample demonstrates how to use image multi-modality with an AI agent. It sh
 Before running this sample, ensure you have:
 
 1. An Azure OpenAI project set up
-2. A compatible model deployment (e.g., gpt-4o)
+2. A compatible model deployment (e.g., gpt-5.4-mini)
 3. Azure CLI installed and authenticated
 
 ## Environment Variables
@@ -29,7 +29,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o" # Replace with your model deployment name (optional, defaults to gpt-4o)
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini" # Replace with your model deployment name (optional, defaults to gpt-5.4-mini)
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step09_AsFunctionTool/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step09_AsFunctionTool/Program.cs
index aca1a95ce4..a6d6f06a36 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step09_AsFunctionTool/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step09_AsFunctionTool/Program.cs
@@ -10,7 +10,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 [Description("Get the weather for a given location.")]
 static string GetWeather([Description("The location to get the weather for.")] string location)
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step10_BackgroundResponsesWithToolsAndPersistence/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step10_BackgroundResponsesWithToolsAndPersistence/Program.cs
index b568ef5867..844b40e405 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step10_BackgroundResponsesWithToolsAndPersistence/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step10_BackgroundResponsesWithToolsAndPersistence/Program.cs
@@ -15,7 +15,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Responses;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 var stateStore = new Dictionary<string, JsonElement?>();
 
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step10_BackgroundResponsesWithToolsAndPersistence/README.md b/dotnet/samples/02-agents/Agents/Agent_Step10_BackgroundResponsesWithToolsAndPersistence/README.md
index ca52e8afa3..b5be2cdd4c 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step10_BackgroundResponsesWithToolsAndPersistence/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step10_BackgroundResponsesWithToolsAndPersistence/README.md
@@ -24,5 +24,5 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5"  # Optional, defaults to gpt-5
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step11_Middleware/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step11_Middleware/Program.cs
index f7f3602fd3..2ffc968d84 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step11_Middleware/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step11_Middleware/Program.cs
@@ -15,7 +15,7 @@ using Microsoft.Extensions.AI;
 
 // Get Microsoft Foundry configuration from environment variables
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = System.Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o";
+var deploymentName = System.Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Get a client to create/retrieve server side agents with
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step11_Middleware/README.md b/dotnet/samples/02-agents/Agents/Agent_Step11_Middleware/README.md
index 74895e0cdf..b03f027fc2 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step11_Middleware/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step11_Middleware/README.md
@@ -27,7 +27,7 @@ Attempting to use function middleware on agents that do not wrap a ChatClientAge
 
 1. Environment variables:
    - `AZURE_OPENAI_ENDPOINT`: Your Azure OpenAI endpoint
-   - `AZURE_OPENAI_DEPLOYMENT_NAME`: Chat deployment name (optional; defaults to `gpt-4o`)
+   - `AZURE_OPENAI_DEPLOYMENT_NAME`: Chat deployment name (optional; defaults to `gpt-5.4-mini`)
 2. Sign in with Azure CLI (PowerShell):
    ```powershell
    az login
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step12_Plugins/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step12_Plugins/Program.cs
index 2e9b405183..15771197d2 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step12_Plugins/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step12_Plugins/Program.cs
@@ -17,7 +17,7 @@ using Microsoft.Extensions.DependencyInjection;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create a service collection to hold the agent plugin and its dependencies.
 ServiceCollection services = new();
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step13_ChatReduction/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step13_ChatReduction/Program.cs
index 915bc5c376..dccb13beaf 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step13_ChatReduction/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step13_ChatReduction/Program.cs
@@ -12,7 +12,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Construct the agent, and provide a factory to create an in-memory chat message store with a reducer that keeps only the last 2 non-system messages.
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step14_BackgroundResponses/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step14_BackgroundResponses/Program.cs
index f474b938a6..215a790fb7 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step14_BackgroundResponses/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step14_BackgroundResponses/Program.cs
@@ -8,7 +8,7 @@ using Microsoft.Agents.AI;
 using OpenAI.Responses;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step14_BackgroundResponses/README.md b/dotnet/samples/02-agents/Agents/Agent_Step14_BackgroundResponses/README.md
index e898733bc3..2a668f9e6c 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step14_BackgroundResponses/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step14_BackgroundResponses/README.md
@@ -23,5 +23,5 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
\ No newline at end of file
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step15_DeepResearch/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step15_DeepResearch/Program.cs
index d329816f13..92222f64e7 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step15_DeepResearch/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step15_DeepResearch/Program.cs
@@ -10,7 +10,7 @@ using Microsoft.Agents.AI;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
 var deepResearchDeploymentName = Environment.GetEnvironmentVariable("AZURE_AI_REASONING_DEPLOYMENT_NAME") ?? "o3-deep-research";
-var modelDeploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o";
+var modelDeploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var bingConnectionId = Environment.GetEnvironmentVariable("AZURE_AI_BING_CONNECTION_ID") ?? throw new InvalidOperationException("AZURE_AI_BING_CONNECTION_ID is not set.");
 
 // Configure extended network timeout for long-running Deep Research tasks.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step15_DeepResearch/README.md b/dotnet/samples/02-agents/Agents/Agent_Step15_DeepResearch/README.md
index b04e65cafc..ee3c0935a2 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step15_DeepResearch/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step15_DeepResearch/README.md
@@ -13,7 +13,7 @@ Before running this sample, ensure you have:
 
 1. A Microsoft Foundry project set up
 2. A deep research model deployment (e.g., o3-deep-research)
-3. A model deployment (e.g., gpt-4o)
+3. A model deployment (e.g., gpt-5.4-mini)
 4. A Bing Connection configured in your Microsoft Foundry project
 5. Azure CLI installed and authenticated
 
@@ -45,5 +45,5 @@ $env:AZURE_AI_BING_CONNECTION_ID="/subscriptions/<sub-id>/resourceGroups/<rg>/pr
 # Optional, defaults to o3-deep-research
 $env:AZURE_AI_REASONING_DEPLOYMENT_NAME="o3-deep-research"
 
-# Optional, defaults to gpt-4o
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o"
+# Optional, defaults to gpt-5.4-mini
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step16_Declarative/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step16_Declarative/Program.cs
index 215833c795..9fd5f29f93 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step16_Declarative/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step16_Declarative/Program.cs
@@ -8,7 +8,7 @@ using Microsoft.Agents.AI;
 using Microsoft.Extensions.AI;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create the chat client
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step17_AdditionalAIContext/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step17_AdditionalAIContext/Program.cs
index 0fd21833e1..69946be8e6 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step17_AdditionalAIContext/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step17_AdditionalAIContext/Program.cs
@@ -18,7 +18,7 @@ using SampleApp;
 using MEAI = Microsoft.Extensions.AI;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // A sample function to load the next three calendar events for the user.
 Func<Task<string[]>> loadNextThreeCalendarEvents = async () =>
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step18_CompactionPipeline/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step18_CompactionPipeline/Program.cs
index ce0a4a294d..b8d774e74d 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step18_CompactionPipeline/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step18_CompactionPipeline/Program.cs
@@ -16,7 +16,7 @@ using Microsoft.Agents.AI.Compaction;
 using Microsoft.Extensions.AI;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step18_CompactionPipeline/README.md b/dotnet/samples/02-agents/Agents/Agent_Step18_CompactionPipeline/README.md
index 0640a42f21..be4610a152 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step18_CompactionPipeline/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step18_CompactionPipeline/README.md
@@ -68,7 +68,7 @@ Order strategies from **least aggressive** to **most aggressive**. The pipeline
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/"  # Required
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"                       # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"                      # Optional, defaults to gpt-5.4-mini
 ```
 
 ## Running the Sample
@@ -110,7 +110,7 @@ IEnumerable<ChatMessage> compacted = await CompactionProvider.CompactAsync(
 The `SummarizationCompactionStrategy` accepts any `IChatClient`. Use a smaller, cheaper model to reduce summarization cost:
 
 ```csharp
-IChatClient summarizerChatClient = openAIClient.GetChatClient("gpt-4o-mini").AsIChatClient();
+IChatClient summarizerChatClient = openAIClient.GetChatClient("gpt-5.4-mini").AsIChatClient();
 new SummarizationCompactionStrategy(summarizerChatClient, CompactionTriggers.TokensExceed(4000))
 ```
 
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step19_InFunctionLoopCheckpointing/Program.cs b/dotnet/samples/02-agents/Agents/Agent_Step19_InFunctionLoopCheckpointing/Program.cs
index 4e526f8f41..18f4eccd5f 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step19_InFunctionLoopCheckpointing/Program.cs
+++ b/dotnet/samples/02-agents/Agents/Agent_Step19_InFunctionLoopCheckpointing/Program.cs
@@ -23,7 +23,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Responses;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var store = Environment.GetEnvironmentVariable("AZURE_OPENAI_RESPONSES_STORE") ?? "false";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/Agents/Agent_Step19_InFunctionLoopCheckpointing/README.md b/dotnet/samples/02-agents/Agents/Agent_Step19_InFunctionLoopCheckpointing/README.md
index 9b96562a66..25ac616275 100644
--- a/dotnet/samples/02-agents/Agents/Agent_Step19_InFunctionLoopCheckpointing/README.md
+++ b/dotnet/samples/02-agents/Agents/Agent_Step19_InFunctionLoopCheckpointing/README.md
@@ -45,7 +45,7 @@ ChatClientAgent
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/"  # Required
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"                       # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"                      # Optional, defaults to gpt-5.4-mini
 ```
 
 ## Running the Sample
diff --git a/dotnet/samples/02-agents/Agents/README.md b/dotnet/samples/02-agents/Agents/README.md
index 6cdf80625b..f429d8156c 100644
--- a/dotnet/samples/02-agents/Agents/README.md
+++ b/dotnet/samples/02-agents/Agents/README.md
@@ -59,7 +59,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
 
 If the variables are not set, you will be prompted for the values when running the samples.
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step00_FoundryAgentLifecycle/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step00_FoundryAgentLifecycle/Program.cs
index 9a22d1cddf..0803418ca4 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step00_FoundryAgentLifecycle/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step00_FoundryAgentLifecycle/Program.cs
@@ -10,7 +10,7 @@ using Azure.Identity;
 using Microsoft.Agents.AI.Foundry;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 const string JokerName = "JokerAgent";
 
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step00_FoundryAgentLifecycle/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step00_FoundryAgentLifecycle/README.md
index 738a1d2e42..8179c3b299 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step00_FoundryAgentLifecycle/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step00_FoundryAgentLifecycle/README.md
@@ -5,7 +5,7 @@ This sample demonstrates the full lifecycle of a `FoundryAgent` backed by a serv
 ## Prerequisites
 
 - A Microsoft Foundry project endpoint
-- A model deployment name (defaults to `gpt-4o-mini`)
+- A model deployment name (defaults to `gpt-5.4-mini`)
 - Azure CLI installed and authenticated
 
 ## Environment Variables
@@ -13,7 +13,7 @@ This sample demonstrates the full lifecycle of a `FoundryAgent` backed by a serv
 | Variable | Description | Required |
 | --- | --- | --- |
 | `AZURE_AI_PROJECT_ENDPOINT` | Microsoft Foundry project endpoint | Yes |
-| `AZURE_AI_MODEL_DEPLOYMENT_NAME` | Model deployment name | No (defaults to `gpt-4o-mini`) |
+| `AZURE_AI_MODEL_DEPLOYMENT_NAME` | Model deployment name | No (defaults to `gpt-5.4-mini`) |
 
 ## Running the sample
 
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step01_Basics/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step01_Basics/Program.cs
index cd89116db7..403bae05c2 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step01_Basics/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step01_Basics/Program.cs
@@ -7,7 +7,7 @@ using Azure.Identity;
 using Microsoft.Agents.AI;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step01_Basics/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step01_Basics/README.md
index 88eebb2a82..612bd21891 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step01_Basics/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step01_Basics/README.md
@@ -22,7 +22,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.1_MultiturnConversation/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.1_MultiturnConversation/Program.cs
index 15b880102f..e00982199f 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.1_MultiturnConversation/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.1_MultiturnConversation/Program.cs
@@ -8,7 +8,7 @@ using Azure.Identity;
 using Microsoft.Agents.AI;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.1_MultiturnConversation/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.1_MultiturnConversation/README.md
index a895981952..f34c486b53 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.1_MultiturnConversation/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.1_MultiturnConversation/README.md
@@ -23,7 +23,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.2_MultiturnWithServerConversations/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.2_MultiturnWithServerConversations/Program.cs
index 6057d71895..317474aa6e 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.2_MultiturnWithServerConversations/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.2_MultiturnWithServerConversations/Program.cs
@@ -10,7 +10,7 @@ using Azure.Identity;
 using Microsoft.Agents.AI;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.2_MultiturnWithServerConversations/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.2_MultiturnWithServerConversations/README.md
index 9d35133b39..ee91d935ef 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.2_MultiturnWithServerConversations/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step02.2_MultiturnWithServerConversations/README.md
@@ -23,7 +23,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step03_UsingFunctionTools/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step03_UsingFunctionTools/Program.cs
index 7935835a24..e1b4548a04 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step03_UsingFunctionTools/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step03_UsingFunctionTools/Program.cs
@@ -16,7 +16,7 @@ static string GetWeather([Description("The location to get the weather for.")] s
 AITool tool = AIFunctionFactory.Create(GetWeather);
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step03_UsingFunctionTools/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step03_UsingFunctionTools/README.md
index 9aa2a4ee69..dfad8d0b5c 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step03_UsingFunctionTools/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step03_UsingFunctionTools/README.md
@@ -24,7 +24,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step04_UsingFunctionToolsWithApprovals/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step04_UsingFunctionToolsWithApprovals/Program.cs
index 9a85dba83b..3943f32295 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step04_UsingFunctionToolsWithApprovals/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step04_UsingFunctionToolsWithApprovals/Program.cs
@@ -13,7 +13,7 @@ static string GetWeather([Description("The location to get the weather for.")] s
     => $"The weather in {location} is cloudy with a high of 15°C.";
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step04_UsingFunctionToolsWithApprovals/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step04_UsingFunctionToolsWithApprovals/README.md
index 430c57548d..a832d308e9 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step04_UsingFunctionToolsWithApprovals/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step04_UsingFunctionToolsWithApprovals/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step05_StructuredOutput/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step05_StructuredOutput/Program.cs
index 28cd4cf6bc..07636f12dd 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step05_StructuredOutput/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step05_StructuredOutput/Program.cs
@@ -13,7 +13,7 @@ using SampleApp;
 #pragma warning disable CA5399
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step05_StructuredOutput/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step05_StructuredOutput/README.md
index f5421b3f64..f2770d6055 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step05_StructuredOutput/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step05_StructuredOutput/README.md
@@ -18,7 +18,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step06_PersistedConversations/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step06_PersistedConversations/Program.cs
index c9774cb1bf..18ce97ef88 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step06_PersistedConversations/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step06_PersistedConversations/Program.cs
@@ -8,7 +8,7 @@ using Azure.Identity;
 using Microsoft.Agents.AI;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step06_PersistedConversations/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step06_PersistedConversations/README.md
index a8cfda07ca..42074f2972 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step06_PersistedConversations/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step06_PersistedConversations/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step07_Observability/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step07_Observability/Program.cs
index 68bfb91af0..e4b451fea3 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step07_Observability/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step07_Observability/Program.cs
@@ -11,7 +11,7 @@ using OpenTelemetry.Trace;
 
 string? applicationInsightsConnectionString = Environment.GetEnvironmentVariable("APPLICATIONINSIGHTS_CONNECTION_STRING");
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create TracerProvider with console exporter.
 string sourceName = Guid.NewGuid().ToString("N");
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step07_Observability/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step07_Observability/README.md
index cb3bb729ff..70e10d805b 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step07_Observability/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step07_Observability/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 $env:APPLICATIONINSIGHTS_CONNECTION_STRING="..."  # Optional
 ```
 
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step08_DependencyInjection/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step08_DependencyInjection/Program.cs
index 52a7d73132..019323e56f 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step08_DependencyInjection/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step08_DependencyInjection/Program.cs
@@ -10,7 +10,7 @@ using Microsoft.Extensions.Hosting;
 using SampleApp;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step08_DependencyInjection/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step08_DependencyInjection/README.md
index c9ad936fd6..52bb3f591e 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step08_DependencyInjection/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step08_DependencyInjection/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step09_UsingMcpClientAsTools/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step09_UsingMcpClientAsTools/Program.cs
index 87f80297af..b07917ee01 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step09_UsingMcpClientAsTools/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step09_UsingMcpClientAsTools/Program.cs
@@ -10,7 +10,7 @@ using Microsoft.Extensions.AI;
 using ModelContextProtocol.Client;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Connect to the Microsoft Learn MCP server via HTTP (Streamable HTTP transport).
 Console.WriteLine("Connecting to MCP server at https://learn.microsoft.com/api/mcp ...");
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step09_UsingMcpClientAsTools/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step09_UsingMcpClientAsTools/README.md
index 72437e0802..ae7fffcb2a 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step09_UsingMcpClientAsTools/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step09_UsingMcpClientAsTools/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step10_UsingImages/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step10_UsingImages/Program.cs
index 2fdc150be9..076237c072 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step10_UsingImages/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step10_UsingImages/Program.cs
@@ -8,7 +8,7 @@ using Microsoft.Agents.AI;
 using Microsoft.Extensions.AI;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step10_UsingImages/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step10_UsingImages/README.md
index 370bf896cf..12d5fb6284 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step10_UsingImages/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step10_UsingImages/README.md
@@ -12,14 +12,14 @@ This sample demonstrates how to use image multi-modality with an agent.
 ## Prerequisites
 
 - .NET 10 SDK or later
-- Microsoft Foundry service endpoint and a vision-capable model deployment (e.g., `gpt-4o`)
+- Microsoft Foundry service endpoint and a vision-capable model deployment (e.g., `gpt-5.4-mini`)
 - Azure CLI installed and authenticated (`az login`)
 
 Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step11_AsFunctionTool/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step11_AsFunctionTool/Program.cs
index 3715ab194f..06d2a4dc18 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step11_AsFunctionTool/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step11_AsFunctionTool/Program.cs
@@ -13,7 +13,7 @@ static string GetWeather([Description("The location to get the weather for.")] s
     => $"The weather in {location} is cloudy with a high of 15°C.";
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step11_AsFunctionTool/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step11_AsFunctionTool/README.md
index 7d361305b9..4fe155d76d 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step11_AsFunctionTool/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step11_AsFunctionTool/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step12_Middleware/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step12_Middleware/Program.cs
index e37bf89639..27240b8372 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step12_Middleware/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step12_Middleware/Program.cs
@@ -21,7 +21,7 @@ static string GetDateTime()
     => DateTimeOffset.Now.ToString();
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step12_Middleware/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step12_Middleware/README.md
index 26b12a22b8..45543329bc 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step12_Middleware/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step12_Middleware/README.md
@@ -20,7 +20,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step13_Plugins/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step13_Plugins/Program.cs
index 3af63090c5..966a7bba12 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step13_Plugins/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step13_Plugins/Program.cs
@@ -17,7 +17,7 @@ using Microsoft.Extensions.DependencyInjection;
 using SampleApp;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 const string AssistantInstructions = "You are a helpful assistant that helps people find information.";
 const string AssistantName = "PluginAssistant";
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step13_Plugins/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step13_Plugins/README.md
index 8cc2f59116..e10025b7f3 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step13_Plugins/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step13_Plugins/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step14_CodeInterpreter/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step14_CodeInterpreter/Program.cs
index 8d7f598a4a..c4661ae49e 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step14_CodeInterpreter/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step14_CodeInterpreter/Program.cs
@@ -13,7 +13,7 @@ const string AgentInstructions = "You are a personal math tutor. When asked a ma
 const string AgentName = "CoderAgent-RAPI";
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step14_CodeInterpreter/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step14_CodeInterpreter/README.md
index 1a8cfc8aae..db63f82e9c 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step14_CodeInterpreter/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step14_CodeInterpreter/README.md
@@ -18,7 +18,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step16_FileSearch/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step16_FileSearch/Program.cs
index c01a951df4..1a2d870342 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step16_FileSearch/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step16_FileSearch/Program.cs
@@ -10,7 +10,7 @@ using OpenAI.Assistants;
 using OpenAI.Files;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 const string AgentInstructions = "You are a helpful assistant that can search through uploaded files to answer questions.";
 
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step16_FileSearch/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step16_FileSearch/README.md
index 5ce7f11cda..45818ca354 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step16_FileSearch/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step16_FileSearch/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step17_OpenAPITools/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step17_OpenAPITools/Program.cs
index 1968b89ca1..d47f4b0078 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step17_OpenAPITools/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step17_OpenAPITools/Program.cs
@@ -10,7 +10,7 @@ using Microsoft.Agents.AI.Foundry;
 using Microsoft.Extensions.AI;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 const string AgentInstructions = "You are a helpful assistant that can use the countries API to retrieve information about countries by their currency code.";
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step17_OpenAPITools/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step17_OpenAPITools/README.md
index 52a11ec1dd..05227fdd98 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step17_OpenAPITools/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step17_OpenAPITools/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step18_BingCustomSearch/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step18_BingCustomSearch/Program.cs
index e244bb3cb0..11048c8154 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step18_BingCustomSearch/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step18_BingCustomSearch/Program.cs
@@ -22,7 +22,7 @@ BingCustomSearchToolOptions bingCustomSearchToolParameters = new([
 ]);
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step18_BingCustomSearch/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step18_BingCustomSearch/README.md
index fc48fd8744..18bffeacd6 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step18_BingCustomSearch/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step18_BingCustomSearch/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 $env:AZURE_AI_CUSTOM_SEARCH_CONNECTION_ID="your-connection-id"  # The full ARM resource URI, e.g., "/subscriptions/.../connections/your-bing-connection"
 $env:AZURE_AI_CUSTOM_SEARCH_INSTANCE_NAME="your-instance-name"  # The Bing Custom Search configuration name (from Azure portal)
 ```
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step19_SharePoint/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step19_SharePoint/Program.cs
index a5f8bf845a..186acb9da5 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step19_SharePoint/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step19_SharePoint/Program.cs
@@ -20,7 +20,7 @@ var sharepointOptions = new SharePointGroundingToolOptions();
 sharepointOptions.ProjectConnections.Add(new ToolProjectConnection(sharepointConnectionId));
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step19_SharePoint/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step19_SharePoint/README.md
index bfaacee860..1049eb4ebc 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step19_SharePoint/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step19_SharePoint/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 $env:SHAREPOINT_PROJECT_CONNECTION_ID="your-sharepoint-connection-id"  # The full ARM resource URI, e.g., "/subscriptions/.../connections/SharepointTestTool"
 ```
 
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step20_MicrosoftFabric/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step20_MicrosoftFabric/Program.cs
index 69954b9483..ccc3c0dcf0 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step20_MicrosoftFabric/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step20_MicrosoftFabric/Program.cs
@@ -17,7 +17,7 @@ var fabricToolOptions = new FabricDataAgentToolOptions();
 fabricToolOptions.ProjectConnections.Add(new ToolProjectConnection(fabricConnectionId));
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step20_MicrosoftFabric/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step20_MicrosoftFabric/README.md
index 4a4d31e151..03536262d2 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step20_MicrosoftFabric/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step20_MicrosoftFabric/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 $env:FABRIC_PROJECT_CONNECTION_ID="your-fabric-connection-id"  # The full ARM resource URI, e.g., "/subscriptions/.../connections/FabricTestTool"
 ```
 
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step21_WebSearch/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step21_WebSearch/Program.cs
index 20d74b0401..da1652536b 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step21_WebSearch/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step21_WebSearch/Program.cs
@@ -12,7 +12,7 @@ const string AgentInstructions = "You are a helpful assistant that can search th
 const string AgentName = "WebSearchAgent-RAPI";
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step21_WebSearch/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step21_WebSearch/README.md
index 1a9d80106d..81d37e6ff5 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step21_WebSearch/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step21_WebSearch/README.md
@@ -18,7 +18,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step22_MemorySearch/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step22_MemorySearch/Program.cs
index b00cc2f801..5ba9ccedb1 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step22_MemorySearch/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step22_MemorySearch/Program.cs
@@ -15,7 +15,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Responses;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 string embeddingModelName = Environment.GetEnvironmentVariable("AZURE_AI_EMBEDDING_DEPLOYMENT_NAME") ?? "text-embedding-ada-002";
 string memoryStoreName = Environment.GetEnvironmentVariable("AZURE_AI_MEMORY_STORE_ID") ?? $"foundry-memory-sample-{Guid.NewGuid():N}";
 
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step22_MemorySearch/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step22_MemorySearch/README.md
index b8020553af..63af9cd9c8 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step22_MemorySearch/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step22_MemorySearch/README.md
@@ -20,7 +20,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 $env:AZURE_AI_MEMORY_STORE_ID="your-memory-store-name"
 ```
 
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step23_LocalMCP/Program.cs b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step23_LocalMCP/Program.cs
index c9f8c0060b..772d1a17f9 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step23_LocalMCP/Program.cs
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step23_LocalMCP/Program.cs
@@ -31,7 +31,7 @@ Console.WriteLine($"MCP tools available: {string.Join(", ", mcpTools.Select(t =>
 List<AITool> wrappedTools = mcpTools.Select(tool => (AITool)new LoggingMcpTool(tool)).ToList();
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step23_LocalMCP/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step23_LocalMCP/README.md
index 84456df2b7..c3464efe5d 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step23_LocalMCP/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/Agent_Step23_LocalMCP/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## Run the sample
diff --git a/dotnet/samples/02-agents/AgentsWithFoundry/README.md b/dotnet/samples/02-agents/AgentsWithFoundry/README.md
index 8cc964e227..c65cb24acd 100644
--- a/dotnet/samples/02-agents/AgentsWithFoundry/README.md
+++ b/dotnet/samples/02-agents/AgentsWithFoundry/README.md
@@ -10,7 +10,7 @@ The simplest way to create a Foundry agent is using the `FoundryAgent` type dire
 FoundryAgent agent = new(
     new Uri(endpoint),
     new AzureCliCredential(),
-    model: "gpt-4o-mini",
+    model: "gpt-5.4-mini",
     instructions: "You are good at telling jokes.",
     name: "JokerAgent");
 
@@ -38,7 +38,7 @@ Set:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project"
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 Some samples require extra tool-specific environment variables. See each sample for details.
diff --git a/dotnet/samples/02-agents/DeclarativeAgents/ChatClient/Program.cs b/dotnet/samples/02-agents/DeclarativeAgents/ChatClient/Program.cs
index 270acfb946..78634eb62d 100644
--- a/dotnet/samples/02-agents/DeclarativeAgents/ChatClient/Program.cs
+++ b/dotnet/samples/02-agents/DeclarativeAgents/ChatClient/Program.cs
@@ -9,7 +9,7 @@ using Microsoft.Agents.AI;
 using Microsoft.Extensions.AI;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create the chat client
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/DevUI/DevUI_Step01_BasicUsage/Program.cs b/dotnet/samples/02-agents/DevUI/DevUI_Step01_BasicUsage/Program.cs
index d35c1385cc..ca3e38ad24 100644
--- a/dotnet/samples/02-agents/DevUI/DevUI_Step01_BasicUsage/Program.cs
+++ b/dotnet/samples/02-agents/DevUI/DevUI_Step01_BasicUsage/Program.cs
@@ -44,7 +44,7 @@ internal static class Program
 
         // Set up the Azure OpenAI client
         var endpoint = builder.Configuration["AZURE_OPENAI_ENDPOINT"] ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = builder.Configuration["AZURE_OPENAI_DEPLOYMENT_NAME"] ?? "gpt-4o-mini";
+        var deploymentName = builder.Configuration["AZURE_OPENAI_DEPLOYMENT_NAME"] ?? "gpt-5.4-mini";
 
         // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
         // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/02-agents/DevUI/DevUI_Step01_BasicUsage/README.md b/dotnet/samples/02-agents/DevUI/DevUI_Step01_BasicUsage/README.md
index 0bf24dfb26..48deaad94e 100644
--- a/dotnet/samples/02-agents/DevUI/DevUI_Step01_BasicUsage/README.md
+++ b/dotnet/samples/02-agents/DevUI/DevUI_Step01_BasicUsage/README.md
@@ -11,7 +11,7 @@ The DevUI provides an interactive web interface for testing and debugging AI age
 Set the following environment variables:
 
 - `AZURE_OPENAI_ENDPOINT` - Your Azure OpenAI endpoint URL (required)
-- `AZURE_OPENAI_DEPLOYMENT_NAME` - Your deployment name (defaults to "gpt-4o-mini")
+- `AZURE_OPENAI_DEPLOYMENT_NAME` - Your deployment name (defaults to "gpt-5.4-mini")
 
 ## Running the Sample
 
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server/Program.cs b/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server/Program.cs
index d773332fdd..d1e80b65df 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server/Program.cs
+++ b/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server/Program.cs
@@ -10,7 +10,7 @@ using ModelContextProtocol.Client;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create an MCPClient for the GitHub server
 await using var mcpClient = await McpClient.CreateAsync(new StdioClientTransport(new()
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server/README.md b/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server/README.md
index 426bb67a97..2c6503e998 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server/README.md
+++ b/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server/README.md
@@ -19,7 +19,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
 
 ## Setup and Running
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/Program.cs b/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/Program.cs
index d741d60701..aaa4b0d11a 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/Program.cs
+++ b/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/Program.cs
@@ -14,7 +14,7 @@ using ModelContextProtocol.Client;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // We can customize a shared HttpClient with a custom handler if desired
 using var sharedHandler = new SocketsHttpHandler
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/README.md b/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/README.md
index 7c646ec915..59c0af0c3f 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/README.md
+++ b/dotnet/samples/02-agents/ModelContextProtocol/Agent_MCP_Server_Auth/README.md
@@ -27,7 +27,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
 
 ## Setup and Running
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/Program.cs b/dotnet/samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/Program.cs
index 7d64ad9399..ce27d036f9 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/Program.cs
+++ b/dotnet/samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/Program.cs
@@ -12,7 +12,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Responses;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT") ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-var model = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4.1-mini";
+var model = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Get a client to create/retrieve server side agents with.
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/README.md b/dotnet/samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/README.md
index d03833b826..c1a62a9080 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/README.md
+++ b/dotnet/samples/02-agents/ModelContextProtocol/FoundryAgent_Hosted_MCP/README.md
@@ -12,5 +12,5 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-foundry-service.services.ai.azure.com/api/projects/your-foundry-project" # Replace with your Microsoft Foundry resource endpoint
-$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-4.1-mini"  # Optional, defaults to gpt-4.1-mini
+$env:AZURE_AI_MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/README.md b/dotnet/samples/02-agents/ModelContextProtocol/README.md
index 9cbaecad4b..8c94ebc027 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/README.md
+++ b/dotnet/samples/02-agents/ModelContextProtocol/README.md
@@ -35,7 +35,7 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
 
 If the variables are not set, you will be prompted for the values when running the samples.
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/ResponseAgent_Hosted_MCP/Program.cs b/dotnet/samples/02-agents/ModelContextProtocol/ResponseAgent_Hosted_MCP/Program.cs
index f8715e4543..59d47d57b1 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/ResponseAgent_Hosted_MCP/Program.cs
+++ b/dotnet/samples/02-agents/ModelContextProtocol/ResponseAgent_Hosted_MCP/Program.cs
@@ -11,7 +11,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Responses;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // **** MCP Tool with Auto Approval ****
 // *************************************
diff --git a/dotnet/samples/02-agents/ModelContextProtocol/ResponseAgent_Hosted_MCP/README.md b/dotnet/samples/02-agents/ModelContextProtocol/ResponseAgent_Hosted_MCP/README.md
index c311edae40..6094a20304 100644
--- a/dotnet/samples/02-agents/ModelContextProtocol/ResponseAgent_Hosted_MCP/README.md
+++ b/dotnet/samples/02-agents/ModelContextProtocol/ResponseAgent_Hosted_MCP/README.md
@@ -13,5 +13,5 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4.1-mini"  # Optional, defaults to gpt-4.1-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
diff --git a/dotnet/samples/03-workflows/Agents/CustomAgentExecutors/Program.cs b/dotnet/samples/03-workflows/Agents/CustomAgentExecutors/Program.cs
index 41b622fdad..eb5cb2db94 100644
--- a/dotnet/samples/03-workflows/Agents/CustomAgentExecutors/Program.cs
+++ b/dotnet/samples/03-workflows/Agents/CustomAgentExecutors/Program.cs
@@ -33,7 +33,7 @@ public static class Program
     {
         // Set up the Azure OpenAI client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         // Create the executors
diff --git a/dotnet/samples/03-workflows/Agents/FoundryAgent/Program.cs b/dotnet/samples/03-workflows/Agents/FoundryAgent/Program.cs
index 458c280ca1..cab2e0162d 100644
--- a/dotnet/samples/03-workflows/Agents/FoundryAgent/Program.cs
+++ b/dotnet/samples/03-workflows/Agents/FoundryAgent/Program.cs
@@ -25,7 +25,7 @@ public static class Program
         // Set up the Azure AI Project client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT")
             ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var aiProjectClient = new AIProjectClient(new Uri(endpoint), new AzureCliCredential());
 
         // Create agents
diff --git a/dotnet/samples/03-workflows/Agents/GroupChatToolApproval/Program.cs b/dotnet/samples/03-workflows/Agents/GroupChatToolApproval/Program.cs
index a8d42b5342..0b6b821f9f 100644
--- a/dotnet/samples/03-workflows/Agents/GroupChatToolApproval/Program.cs
+++ b/dotnet/samples/03-workflows/Agents/GroupChatToolApproval/Program.cs
@@ -43,7 +43,7 @@ public static class Program
     private static async Task Main()
     {
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
         // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
         // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/03-workflows/Agents/GroupChatToolApproval/README.md b/dotnet/samples/03-workflows/Agents/GroupChatToolApproval/README.md
index f569b836e9..cda9be4673 100644
--- a/dotnet/samples/03-workflows/Agents/GroupChatToolApproval/README.md
+++ b/dotnet/samples/03-workflows/Agents/GroupChatToolApproval/README.md
@@ -45,7 +45,7 @@ The sample demonstrates continuous event-driven execution with inline approval h
 
 - Azure OpenAI or OpenAI configured with the required environment variables
 - `AZURE_OPENAI_ENDPOINT` environment variable set
-- `AZURE_OPENAI_DEPLOYMENT_NAME` environment variable (defaults to "gpt-4o-mini")
+- `AZURE_OPENAI_DEPLOYMENT_NAME` environment variable (defaults to "gpt-5.4-mini")
 
 ## Running the Sample
 
diff --git a/dotnet/samples/03-workflows/Agents/WorkflowAsAnAgent/Program.cs b/dotnet/samples/03-workflows/Agents/WorkflowAsAnAgent/Program.cs
index bc9faff3b0..004267d978 100644
--- a/dotnet/samples/03-workflows/Agents/WorkflowAsAnAgent/Program.cs
+++ b/dotnet/samples/03-workflows/Agents/WorkflowAsAnAgent/Program.cs
@@ -39,7 +39,7 @@ public static class Program
     {
         // Set up the Azure OpenAI client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         // Create the workflow and turn it into an agent
diff --git a/dotnet/samples/03-workflows/Concurrent/Concurrent/Program.cs b/dotnet/samples/03-workflows/Concurrent/Concurrent/Program.cs
index c5f77c80f4..38e89653d6 100644
--- a/dotnet/samples/03-workflows/Concurrent/Concurrent/Program.cs
+++ b/dotnet/samples/03-workflows/Concurrent/Concurrent/Program.cs
@@ -35,7 +35,7 @@ public static class Program
         // Set up the Azure AI Project client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT")
             ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_AI_MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AIProjectClient(new Uri(endpoint), new AzureCliCredential())
                             .ProjectOpenAIClient.GetChatClient(deploymentName).AsIChatClient();
 
diff --git a/dotnet/samples/03-workflows/ConditionalEdges/01_EdgeCondition/Program.cs b/dotnet/samples/03-workflows/ConditionalEdges/01_EdgeCondition/Program.cs
index de4f252deb..370011d80f 100644
--- a/dotnet/samples/03-workflows/ConditionalEdges/01_EdgeCondition/Program.cs
+++ b/dotnet/samples/03-workflows/ConditionalEdges/01_EdgeCondition/Program.cs
@@ -36,7 +36,7 @@ public static class Program
     {
         // Set up the Azure OpenAI client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         // Create agents
diff --git a/dotnet/samples/03-workflows/ConditionalEdges/02_SwitchCase/Program.cs b/dotnet/samples/03-workflows/ConditionalEdges/02_SwitchCase/Program.cs
index 7dd5927711..4e85039af8 100644
--- a/dotnet/samples/03-workflows/ConditionalEdges/02_SwitchCase/Program.cs
+++ b/dotnet/samples/03-workflows/ConditionalEdges/02_SwitchCase/Program.cs
@@ -37,7 +37,7 @@ public static class Program
     {
         // Set up the Azure OpenAI client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         // Create agents
diff --git a/dotnet/samples/03-workflows/ConditionalEdges/03_MultiSelection/Program.cs b/dotnet/samples/03-workflows/ConditionalEdges/03_MultiSelection/Program.cs
index d41c0ff275..3dfb13bf60 100644
--- a/dotnet/samples/03-workflows/ConditionalEdges/03_MultiSelection/Program.cs
+++ b/dotnet/samples/03-workflows/ConditionalEdges/03_MultiSelection/Program.cs
@@ -39,7 +39,7 @@ public static class Program
     {
         // Set up the Azure OpenAI client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         // Create agents
diff --git a/dotnet/samples/03-workflows/Declarative/InvokeMcpTool/InvokeMcpTool.yaml b/dotnet/samples/03-workflows/Declarative/InvokeMcpTool/InvokeMcpTool.yaml
index 7b942cb2bd..a626a0ac11 100644
--- a/dotnet/samples/03-workflows/Declarative/InvokeMcpTool/InvokeMcpTool.yaml
+++ b/dotnet/samples/03-workflows/Declarative/InvokeMcpTool/InvokeMcpTool.yaml
@@ -9,7 +9,7 @@
 # 4. Uses an agent to summarize the results
 #
 # Example input: 
-# gpt-4.1
+# gpt-5.4-mini
 #
 kind: Workflow
 trigger:
diff --git a/dotnet/samples/03-workflows/Declarative/InvokeMcpTool/Program.cs b/dotnet/samples/03-workflows/Declarative/InvokeMcpTool/Program.cs
index 560b6d25ca..24d5a6e267 100644
--- a/dotnet/samples/03-workflows/Declarative/InvokeMcpTool/Program.cs
+++ b/dotnet/samples/03-workflows/Declarative/InvokeMcpTool/Program.cs
@@ -31,7 +31,7 @@ namespace Demo.Workflows.Declarative.InvokeMcpTool;
 /// </list>
 /// <para>
 /// This sample uses the Microsoft Learn MCP server to search Azure documentation and the Microsoft Foundry MCP server to get AI model details.
-/// When you run the sample, provide an AI model (e.g. gpt-4.1-mini) as input,
+/// When you run the sample, provide an AI model (e.g. gpt-5.4-mini) as input,
 /// The workflow will use the MCP tools to find relevant information about the model from Microsoft Learn and foundry, then an agent will summarize the results.
 /// </para>
 /// <para>
diff --git a/dotnet/samples/03-workflows/Observability/WorkflowAsAnAgent/Program.cs b/dotnet/samples/03-workflows/Observability/WorkflowAsAnAgent/Program.cs
index f1911dc43f..acf5d26769 100644
--- a/dotnet/samples/03-workflows/Observability/WorkflowAsAnAgent/Program.cs
+++ b/dotnet/samples/03-workflows/Observability/WorkflowAsAnAgent/Program.cs
@@ -72,7 +72,7 @@ public static class Program
 
         // Set up the Azure OpenAI client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential())
             .GetChatClient(deploymentName)
             .AsIChatClient()
diff --git a/dotnet/samples/03-workflows/_StartHere/02_AgentsInWorkflows/Program.cs b/dotnet/samples/03-workflows/_StartHere/02_AgentsInWorkflows/Program.cs
index 990b5f9f17..d0bc5d4749 100644
--- a/dotnet/samples/03-workflows/_StartHere/02_AgentsInWorkflows/Program.cs
+++ b/dotnet/samples/03-workflows/_StartHere/02_AgentsInWorkflows/Program.cs
@@ -29,7 +29,7 @@ public static class Program
     {
         // Set up the Azure OpenAI client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         // Create agents
diff --git a/dotnet/samples/03-workflows/_StartHere/03_AgentWorkflowPatterns/Program.cs b/dotnet/samples/03-workflows/_StartHere/03_AgentWorkflowPatterns/Program.cs
index a562226740..7e6fb55be7 100644
--- a/dotnet/samples/03-workflows/_StartHere/03_AgentWorkflowPatterns/Program.cs
+++ b/dotnet/samples/03-workflows/_StartHere/03_AgentWorkflowPatterns/Program.cs
@@ -24,7 +24,7 @@ public static class Program
     {
         // Set up the Azure OpenAI client.
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var client = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         Console.Write("Choose workflow type ('sequential', 'concurrent', 'handoffs', 'groupchat'): ");
diff --git a/dotnet/samples/03-workflows/_StartHere/04_MultiModelService/Program.cs b/dotnet/samples/03-workflows/_StartHere/04_MultiModelService/Program.cs
index 148ed039fc..7817c5014b 100644
--- a/dotnet/samples/03-workflows/_StartHere/04_MultiModelService/Program.cs
+++ b/dotnet/samples/03-workflows/_StartHere/04_MultiModelService/Program.cs
@@ -19,7 +19,7 @@ IChatClient anthropic = new Anthropic.AnthropicClient(
 IChatClient openai = new OpenAI.OpenAIClient(
     Environment.GetEnvironmentVariable("OPENAI_API_KEY"))
     .GetResponsesClient()
-    .AsIChatClient("gpt-4o-mini");
+    .AsIChatClient("gpt-5.4-mini");
 
 // Define our agents.
 AIAgent researcher = new ChatClientAgent(google,
diff --git a/dotnet/samples/03-workflows/_StartHere/06_MixedWorkflowAgentsAndExecutors/Program.cs b/dotnet/samples/03-workflows/_StartHere/06_MixedWorkflowAgentsAndExecutors/Program.cs
index c566054146..2359a1f10e 100644
--- a/dotnet/samples/03-workflows/_StartHere/06_MixedWorkflowAgentsAndExecutors/Program.cs
+++ b/dotnet/samples/03-workflows/_StartHere/06_MixedWorkflowAgentsAndExecutors/Program.cs
@@ -42,7 +42,7 @@ public static class Program
 
         // Set up the Azure OpenAI client
         var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         var chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         // Create executors for text processing
diff --git a/dotnet/samples/03-workflows/_StartHere/06_MixedWorkflowAgentsAndExecutors/README.md b/dotnet/samples/03-workflows/_StartHere/06_MixedWorkflowAgentsAndExecutors/README.md
index 5b93a83b6f..8568f8fc44 100644
--- a/dotnet/samples/03-workflows/_StartHere/06_MixedWorkflowAgentsAndExecutors/README.md
+++ b/dotnet/samples/03-workflows/_StartHere/06_MixedWorkflowAgentsAndExecutors/README.md
@@ -77,7 +77,7 @@ Without this adapter, the workflow would fail because the agent cannot accept ra
 - An Azure OpenAI endpoint and deployment
 - Set the following environment variables:
   - `AZURE_OPENAI_ENDPOINT` - Your Azure OpenAI endpoint URL
-  - `AZURE_OPENAI_DEPLOYMENT_NAME` - Your chat completion deployment name (defaults to "gpt-4o-mini")
+  - `AZURE_OPENAI_DEPLOYMENT_NAME` - Your chat completion deployment name (defaults to "gpt-5.4-mini")
 
 ## Running the Sample
 
diff --git a/dotnet/samples/03-workflows/_StartHere/07_WriterCriticWorkflow/Program.cs b/dotnet/samples/03-workflows/_StartHere/07_WriterCriticWorkflow/Program.cs
index f93372bc54..0d8ffbf1cf 100644
--- a/dotnet/samples/03-workflows/_StartHere/07_WriterCriticWorkflow/Program.cs
+++ b/dotnet/samples/03-workflows/_StartHere/07_WriterCriticWorkflow/Program.cs
@@ -49,7 +49,7 @@ public static class Program
 
         // Set up the Azure OpenAI client
         string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-        string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+        string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
         IChatClient chatClient = new AzureOpenAIClient(new Uri(endpoint), new AzureCliCredential()).GetChatClient(deploymentName).AsIChatClient();
 
         // Create executors for content creation and review
diff --git a/dotnet/samples/04-hosting/A2A/A2AAgent_AsFunctionTools/Program.cs b/dotnet/samples/04-hosting/A2A/A2AAgent_AsFunctionTools/Program.cs
index cbb3799274..d0b71ef785 100644
--- a/dotnet/samples/04-hosting/A2A/A2AAgent_AsFunctionTools/Program.cs
+++ b/dotnet/samples/04-hosting/A2A/A2AAgent_AsFunctionTools/Program.cs
@@ -13,7 +13,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var a2aAgentHost = Environment.GetEnvironmentVariable("A2A_AGENT_HOST") ?? throw new InvalidOperationException("A2A_AGENT_HOST is not set.");
 
 // Initialize an A2ACardResolver to get an A2A agent card.
diff --git a/dotnet/samples/04-hosting/A2A/A2AAgent_AsFunctionTools/README.md b/dotnet/samples/04-hosting/A2A/A2AAgent_AsFunctionTools/README.md
index c050ad0830..33b5f692f2 100644
--- a/dotnet/samples/04-hosting/A2A/A2AAgent_AsFunctionTools/README.md
+++ b/dotnet/samples/04-hosting/A2A/A2AAgent_AsFunctionTools/README.md
@@ -18,5 +18,5 @@ Set the following environment variables:
 ```powershell
 $env:A2A_AGENT_HOST="https://your-a2a-agent-host" # Replace with your A2A agent host endpoint
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
 ```
\ No newline at end of file
diff --git a/dotnet/samples/04-hosting/DurableAgents/AzureFunctions/README.md b/dotnet/samples/04-hosting/DurableAgents/AzureFunctions/README.md
index ed34b820d0..2839c67587 100644
--- a/dotnet/samples/04-hosting/DurableAgents/AzureFunctions/README.md
+++ b/dotnet/samples/04-hosting/DurableAgents/AzureFunctions/README.md
@@ -22,7 +22,7 @@ The following prerequisites are required to run the samples:
 - [.NET 10.0 SDK or later](https://dotnet.microsoft.com/download/dotnet)
 - [Azure Functions Core Tools](https://learn.microsoft.com/azure/azure-functions/functions-run-local) (version 4.x or later)
 - [Azure CLI](https://learn.microsoft.com/cli/azure/install-azure-cli) installed and authenticated (`az login`) or an API key for the Azure OpenAI service
-- [Azure OpenAI Service](https://learn.microsoft.com/azure/ai-services/openai/how-to/create-resource) with a deployed model (gpt-4o-mini or better is recommended)
+- [Azure OpenAI Service](https://learn.microsoft.com/azure/ai-services/openai/how-to/create-resource) with a deployed model (gpt-5.4-mini or better is recommended)
 - [Durable Task Scheduler](https://learn.microsoft.com/azure/azure-functions/durable/durable-task-scheduler/develop-with-durable-task-scheduler) (local emulator or Azure-hosted)
 - [Docker](https://docs.docker.com/get-docker/) installed if running the Durable Task Scheduler emulator locally
 
diff --git a/dotnet/samples/04-hosting/DurableAgents/ConsoleApps/README.md b/dotnet/samples/04-hosting/DurableAgents/ConsoleApps/README.md
index 9f52715256..43f988d327 100644
--- a/dotnet/samples/04-hosting/DurableAgents/ConsoleApps/README.md
+++ b/dotnet/samples/04-hosting/DurableAgents/ConsoleApps/README.md
@@ -20,7 +20,7 @@ The following prerequisites are required to run the samples:
 
 - [.NET 10.0 SDK or later](https://dotnet.microsoft.com/download/dotnet)
 - [Azure CLI](https://learn.microsoft.com/cli/azure/install-azure-cli) installed and authenticated (`az login`) or an API key for the Azure OpenAI service
-- [Azure OpenAI Service](https://learn.microsoft.com/azure/ai-services/openai/how-to/create-resource) with a deployed model (gpt-4o-mini or better is recommended)
+- [Azure OpenAI Service](https://learn.microsoft.com/azure/ai-services/openai/how-to/create-resource) with a deployed model (gpt-5.4-mini or better is recommended)
 - [Durable Task Scheduler](https://learn.microsoft.com/azure/azure-functions/durable/durable-task-scheduler/develop-with-durable-task-scheduler) (local emulator or Azure-hosted)
 - [Docker](https://docs.docker.com/get-docker/) installed if running the Durable Task Scheduler emulator locally
 - [Redis](https://redis.io/) (for sample 07 only) - can be run locally using Docker
diff --git a/dotnet/samples/04-hosting/DurableWorkflows/ConsoleApps/02_ConcurrentWorkflow/README.md b/dotnet/samples/04-hosting/DurableWorkflows/ConsoleApps/02_ConcurrentWorkflow/README.md
index 4887a77ccc..a0030058d6 100644
--- a/dotnet/samples/04-hosting/DurableWorkflows/ConsoleApps/02_ConcurrentWorkflow/README.md
+++ b/dotnet/samples/04-hosting/DurableWorkflows/ConsoleApps/02_ConcurrentWorkflow/README.md
@@ -59,7 +59,7 @@ DURABLE_TASK_SCHEDULER_CONNECTION_STRING="Endpoint=http://localhost:8080;TaskHub
 
 # Azure OpenAI (required)
 AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/"
-AZURE_OPENAI_DEPLOYMENT="gpt-4o"
+AZURE_OPENAI_DEPLOYMENT="gpt-5.4-mini"
 AZURE_OPENAI_KEY="your-key"  # Optional if using Azure CLI credentials
 ```
 
diff --git a/dotnet/samples/05-end-to-end/A2AClientServer/A2AClient/Program.cs b/dotnet/samples/05-end-to-end/A2AClientServer/A2AClient/Program.cs
index 0b9696e3a1..3624acd981 100644
--- a/dotnet/samples/05-end-to-end/A2AClientServer/A2AClient/Program.cs
+++ b/dotnet/samples/05-end-to-end/A2AClientServer/A2AClient/Program.cs
@@ -36,7 +36,7 @@ public static class Program
             .AddUserSecrets(Assembly.GetExecutingAssembly())
             .Build();
         var apiKey = configRoot["A2AClient:ApiKey"] ?? throw new ArgumentException("A2AClient:ApiKey must be provided");
-        var modelId = configRoot["A2AClient:ModelId"] ?? "gpt-4.1";
+        var modelId = configRoot["A2AClient:ModelId"] ?? "gpt-5.4-mini";
         var agentUrls = configRoot["A2AClient:AgentUrls"] ?? "http://localhost:5000/;http://localhost:5001/;http://localhost:5002/";
 
         // Create the Host agent
diff --git a/dotnet/samples/05-end-to-end/A2AClientServer/A2AClient/README.md b/dotnet/samples/05-end-to-end/A2AClientServer/A2AClient/README.md
index eb233fb8d1..8e0418c229 100644
--- a/dotnet/samples/05-end-to-end/A2AClientServer/A2AClient/README.md
+++ b/dotnet/samples/05-end-to-end/A2AClientServer/A2AClient/README.md
@@ -20,7 +20,7 @@ The agent urls are provided as a ` ` delimited list of strings
 ```powershell
 cd dotnet/samples/05-end-to-end/A2AClientServer/A2AClient
 
-$env:OPENAI_CHAT_MODEL_NAME="gpt-4o-mini"
+$env:OPENAI_CHAT_MODEL_NAME="gpt-5.4-mini"
 $env:OPENAI_API_KEY="<Your OPENAI api key>"
 $env:AGENT_URLS="http://localhost:5000/policy;http://localhost:5000/invoice;http://localhost:5000/logistics"
 ```
diff --git a/dotnet/samples/05-end-to-end/A2AClientServer/A2AServer/Program.cs b/dotnet/samples/05-end-to-end/A2AClientServer/A2AServer/Program.cs
index f1c0b966fe..8dcb3d1a34 100644
--- a/dotnet/samples/05-end-to-end/A2AClientServer/A2AServer/Program.cs
+++ b/dotnet/samples/05-end-to-end/A2AClientServer/A2AServer/Program.cs
@@ -36,7 +36,7 @@ IConfigurationRoot configuration = new ConfigurationBuilder()
     .Build();
 
 string? apiKey = configuration["OPENAI_API_KEY"];
-string model = configuration["OPENAI_CHAT_MODEL_NAME"] ?? "gpt-4o-mini";
+string model = configuration["OPENAI_CHAT_MODEL_NAME"] ?? "gpt-5.4-mini";
 string? endpoint = configuration["AZURE_AI_PROJECT_ENDPOINT"];
 
 var invoiceQueryPlugin = new InvoiceQuery();
diff --git a/dotnet/samples/05-end-to-end/A2AClientServer/README.md b/dotnet/samples/05-end-to-end/A2AClientServer/README.md
index 1f49d56f80..0efb17e748 100644
--- a/dotnet/samples/05-end-to-end/A2AClientServer/README.md
+++ b/dotnet/samples/05-end-to-end/A2AClientServer/README.md
@@ -206,7 +206,7 @@ Sample output from the A2A client:
 ```
 A2AClient> dotnet run
 info: HostClientAgent[0]
-      Initializing Agent Framework agent with model: gpt-4o-mini
+      Initializing Agent Framework agent with model: gpt-5.4-mini
 
 User (:q or quit to exit): Customer is disputing transaction TICKET-XYZ987 as they claim the received fewer t-shirts than ordered.
 
diff --git a/dotnet/samples/05-end-to-end/AGUIClientServer/README.md b/dotnet/samples/05-end-to-end/AGUIClientServer/README.md
index 2e4887cde9..788ae93d7d 100644
--- a/dotnet/samples/05-end-to-end/AGUIClientServer/README.md
+++ b/dotnet/samples/05-end-to-end/AGUIClientServer/README.md
@@ -19,7 +19,7 @@ Configure the required Azure OpenAI environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="<<your-model-endpoint>>"
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4.1-mini"
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 > **Note:** This sample uses `DefaultAzureCredential` for authentication. Make sure you're authenticated with Azure (e.g., via `az login`, Visual Studio, or environment variables).
diff --git a/dotnet/samples/05-end-to-end/AGUIWebChat/README.md b/dotnet/samples/05-end-to-end/AGUIWebChat/README.md
index 721d1bdf41..96a78e80ac 100644
--- a/dotnet/samples/05-end-to-end/AGUIWebChat/README.md
+++ b/dotnet/samples/05-end-to-end/AGUIWebChat/README.md
@@ -15,7 +15,7 @@ The server requires Azure OpenAI credentials. Set the following environment vari
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/"
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="your-deployment-name"  # e.g., "gpt-4o"
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="your-deployment-name"  # e.g., "gpt-5.4-mini"
 ```
 
 The server uses `DefaultAzureCredential` for authentication. Ensure you are logged in using one of the following methods:
diff --git a/dotnet/samples/05-end-to-end/AgentWebChat/AgentWebChat.AppHost/Program.cs b/dotnet/samples/05-end-to-end/AgentWebChat/AgentWebChat.AppHost/Program.cs
index 328e3f5e83..0f6ead59c9 100644
--- a/dotnet/samples/05-end-to-end/AgentWebChat/AgentWebChat.AppHost/Program.cs
+++ b/dotnet/samples/05-end-to-end/AgentWebChat/AgentWebChat.AppHost/Program.cs
@@ -6,7 +6,7 @@ var builder = DistributedApplication.CreateBuilder(args);
 
 var azOpenAiResource = builder.AddParameterFromConfiguration("AzureOpenAIName", "AzureOpenAI:Name");
 var azOpenAiResourceGroup = builder.AddParameterFromConfiguration("AzureOpenAIResourceGroup", "AzureOpenAI:ResourceGroup");
-var chatModel = builder.AddAIModel("chat-model").AsAzureOpenAI("gpt-4o", o => o.AsExisting(azOpenAiResource, azOpenAiResourceGroup));
+var chatModel = builder.AddAIModel("chat-model").AsAzureOpenAI("gpt-5.4-mini", o => o.AsExisting(azOpenAiResource, azOpenAiResourceGroup));
 
 var agentHost = builder.AddProject<Projects.AgentWebChat_AgentHost>("agenthost")
     .WithHttpEndpoint(name: "devui")
diff --git a/dotnet/samples/05-end-to-end/AgentWithPurview/Program.cs b/dotnet/samples/05-end-to-end/AgentWithPurview/Program.cs
index 33e7001a51..aadb48c635 100644
--- a/dotnet/samples/05-end-to-end/AgentWithPurview/Program.cs
+++ b/dotnet/samples/05-end-to-end/AgentWithPurview/Program.cs
@@ -13,7 +13,7 @@ using Microsoft.Agents.AI.Purview;
 using Microsoft.Extensions.AI;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 var purviewClientAppId = Environment.GetEnvironmentVariable("PURVIEW_CLIENT_APP_ID") ?? throw new InvalidOperationException("PURVIEW_CLIENT_APP_ID is not set.");
 
 // This will get a user token for an entra app configured to call the Purview API.
diff --git a/dotnet/samples/05-end-to-end/AspNetAgentAuthorization/README.md b/dotnet/samples/05-end-to-end/AspNetAgentAuthorization/README.md
index c84dd125c3..56eecb6747 100644
--- a/dotnet/samples/05-end-to-end/AspNetAgentAuthorization/README.md
+++ b/dotnet/samples/05-end-to-end/AspNetAgentAuthorization/README.md
@@ -39,7 +39,7 @@ The AgentService requires an OpenAI-compatible endpoint. Set these environment v
 
 ```bash
 export OPENAI_API_KEY="<your-openai-api-key>"
-export OPENAI_MODEL="gpt-4.1-mini"
+export OPENAI_MODEL="gpt-5.4-mini"
 ```
 
 ## Running the Sample
diff --git a/dotnet/samples/05-end-to-end/AspNetAgentAuthorization/Service/Program.cs b/dotnet/samples/05-end-to-end/AspNetAgentAuthorization/Service/Program.cs
index e443888cea..e348212b37 100644
--- a/dotnet/samples/05-end-to-end/AspNetAgentAuthorization/Service/Program.cs
+++ b/dotnet/samples/05-end-to-end/AspNetAgentAuthorization/Service/Program.cs
@@ -74,7 +74,7 @@ builder.Services.ConfigureHttpJsonOptions(options =>
 // ---------------------------------------------------------------------------
 string apiKey = builder.Configuration["OPENAI_API_KEY"]
     ?? throw new InvalidOperationException("Set the OPENAI_API_KEY environment variable.");
-string model = builder.Configuration["OPENAI_MODEL"] ?? "gpt-4.1-mini";
+string model = builder.Configuration["OPENAI_MODEL"] ?? "gpt-5.4-mini";
 
 // Here we are using Singleton lifetime, since none of the services, function tools and user context classes in the sample have state that are per request.
 // You should evaluate the appropriate lifetime for your own services and tools based on their behavior and dependencies.
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/Program.cs b/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/Program.cs
index c816b018e9..fee781d660 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/Program.cs
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/Program.cs
@@ -14,7 +14,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 [Description("Get the weather for a given location.")]
 static string GetWeather([Description("The location to get the weather for.")] string location)
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/README.md b/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/README.md
index f2d9a65103..465dfacbf0 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/README.md
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/README.md
@@ -15,7 +15,7 @@ Before running this sample, ensure you have:
 
 1. .NET 10 SDK installed
 2. An Azure OpenAI endpoint configured
-3. A deployment of a chat model (e.g., gpt-4o-mini)
+3. A deployment of a chat model (e.g., gpt-5.4-mini)
 4. Azure CLI installed and authenticated (`az login`)
 
 ## Environment Variables
@@ -26,8 +26,8 @@ Set the following environment variables:
 # Replace with your Azure OpenAI endpoint
 $env:AZURE_OPENAI_ENDPOINT="https://your-openai-resource.openai.azure.com/"
 
-# Optional, defaults to gpt-4o-mini
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+# Optional, defaults to gpt-5.4-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## How It Works
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/agent.yaml b/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/agent.yaml
index aa78734283..c7e67b3d4e 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/agent.yaml
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentThreadAndHITL/agent.yaml
@@ -21,8 +21,8 @@ template:
     - name: AZURE_OPENAI_ENDPOINT
       value: ${AZURE_OPENAI_ENDPOINT}
     - name: AZURE_OPENAI_DEPLOYMENT_NAME
-      value: gpt-4o-mini
+      value: gpt-5.4-mini
 resources:
-  - name: "gpt-4o-mini"
+  - name: "gpt-5.4-mini"
     kind: model
-    id: gpt-4o-mini
+    id: gpt-5.4-mini
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/Program.cs b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/Program.cs
index b7b610b663..4178946604 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/Program.cs
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/Program.cs
@@ -15,7 +15,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Responses;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // Create an MCP tool that can be called without approval.
 AITool mcpTool = new HostedMcpServerTool(serverName: "microsoft_learn", serverAddress: "https://learn.microsoft.com/api/mcp")
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/README.md b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/README.md
index 106e08e720..dc0718dfa7 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/README.md
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/README.md
@@ -15,7 +15,7 @@ Key features:
 Before running this sample, ensure you have:
 
 1. An Azure OpenAI endpoint configured
-2. A deployment of a chat model (e.g., gpt-4o-mini)
+2. A deployment of a chat model (e.g., gpt-5.4-mini)
 3. Azure CLI installed and authenticated
 
 **Note**: This sample uses `DefaultAzureCredential` for authentication, which probes multiple sources automatically. For local development, make sure you're logged in with `az login` and have access to the Azure OpenAI resource.
@@ -28,8 +28,8 @@ Set the following environment variables:
 # Replace with your Azure OpenAI endpoint
 $env:AZURE_OPENAI_ENDPOINT="https://your-openai-resource.openai.azure.com/"
 
-# Optional, defaults to gpt-4o-mini
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+# Optional, defaults to gpt-5.4-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## How It Works
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/agent.yaml b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/agent.yaml
index 6444f1aad0..7c02acb02a 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/agent.yaml
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithHostedMCP/agent.yaml
@@ -24,8 +24,8 @@ template:
     - name: AZURE_OPENAI_ENDPOINT
       value: ${AZURE_OPENAI_ENDPOINT}
     - name: AZURE_OPENAI_DEPLOYMENT_NAME
-      value: gpt-4o-mini
+      value: gpt-5.4-mini
 resources:
-  - name: "gpt-4o-mini"
+  - name: "gpt-5.4-mini"
     kind: model
-    id: gpt-4o-mini
+    id: gpt-5.4-mini
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/Program.cs b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/Program.cs
index 329ad74ea2..0da7c57b12 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/Program.cs
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/Program.cs
@@ -17,7 +17,7 @@ using Microsoft.Extensions.AI;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT")
     ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 Console.WriteLine($"Project Endpoint: {endpoint}");
 Console.WriteLine($"Model Deployment: {deploymentName}");
 
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/README.md b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/README.md
index 58ea174718..aba51898ec 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/README.md
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/README.md
@@ -15,7 +15,7 @@ Key features:
 Before running this sample, ensure you have:
 
 1. .NET 10 SDK installed
-2. A Microsoft Foundry Project with a chat model deployed (e.g., gpt-4o-mini)
+2. A Microsoft Foundry Project with a chat model deployed (e.g., gpt-5.4-mini)
 3. Azure CLI installed and authenticated (`az login`)
 
 ## Environment Variables
@@ -26,8 +26,8 @@ Set the following environment variables:
 # Replace with your Microsoft Foundry project endpoint
 $env:AZURE_AI_PROJECT_ENDPOINT="https://your-project.services.ai.azure.com/api/projects/your-project-name"
 
-# Optional, defaults to gpt-4o-mini
-$env:MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+# Optional, defaults to gpt-5.4-mini
+$env:MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## How It Works
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/agent.yaml b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/agent.yaml
index e60d9ccadf..7e75a738ce 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/agent.yaml
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithLocalTools/agent.yaml
@@ -22,8 +22,8 @@ template:
     - name: AZURE_AI_PROJECT_ENDPOINT
       value: ${AZURE_AI_PROJECT_ENDPOINT}
     - name: MODEL_DEPLOYMENT_NAME
-      value: gpt-4o-mini
+      value: gpt-5.4-mini
 resources:
   - kind: model
-    id: gpt-4o-mini
+    id: gpt-5.4-mini
     name: chat
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/Program.cs b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/Program.cs
index bb28fc0d9b..518ce5679f 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/Program.cs
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/Program.cs
@@ -12,7 +12,7 @@ using Microsoft.Extensions.AI;
 using OpenAI.Chat;
 
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 TextSearchProviderOptions textSearchOptions = new()
 {
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/README.md b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/README.md
index 396bc1bc9b..b62d9068ce 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/README.md
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/README.md
@@ -15,7 +15,7 @@ Key features:
 Before running this sample, ensure you have:
 
 1. An Azure OpenAI endpoint configured
-2. A deployment of a chat model (e.g., gpt-4o-mini)
+2. A deployment of a chat model (e.g., gpt-5.4-mini)
 3. Azure CLI installed and authenticated
 
 ## Environment Variables
@@ -26,8 +26,8 @@ Set the following environment variables:
 # Replace with your Azure OpenAI endpoint
 $env:AZURE_OPENAI_ENDPOINT="https://your-openai-resource.openai.azure.com/"
 
-# Optional, defaults to gpt-4o-mini
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"
+# Optional, defaults to gpt-5.4-mini
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ## How It Works
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/agent.yaml b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/agent.yaml
index 1366071b17..6cdad09e9c 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/agent.yaml
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentWithTextSearchRag/agent.yaml
@@ -24,8 +24,8 @@ template:
     - name: AZURE_OPENAI_ENDPOINT
       value: ${AZURE_OPENAI_ENDPOINT}
     - name: AZURE_OPENAI_DEPLOYMENT_NAME
-      value: gpt-4o-mini
+      value: gpt-5.4-mini
 resources:
-  - name: "gpt-4o-mini"
+  - name: "gpt-5.4-mini"
     kind: model
-    id: gpt-4o-mini
+    id: gpt-5.4-mini
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/Program.cs b/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/Program.cs
index f5ea72e7f7..886e205acf 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/Program.cs
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/Program.cs
@@ -13,7 +13,7 @@ using Microsoft.Extensions.AI;
 
 // Set up the Azure OpenAI client
 string endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT") ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+string deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/README.md b/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/README.md
index 0f2f188f1b..b7a2f9ca53 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/README.md
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/README.md
@@ -25,4 +25,4 @@ Set the following environment variables:
 
 ```powershell
 $env:AZURE_OPENAI_ENDPOINT="https://your-resource.openai.azure.com/" # Replace with your Azure OpenAI resource endpoint
-$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-4o-mini"  # Optional, defaults to gpt-4o-mini
\ No newline at end of file
+$env:AZURE_OPENAI_DEPLOYMENT_NAME="gpt-5.4-mini"  # Optional, defaults to gpt-5.4-mini
\ No newline at end of file
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/agent.yaml b/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/agent.yaml
index 900f05d513..3c97fa2ac1 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/agent.yaml
+++ b/dotnet/samples/05-end-to-end/HostedAgents/AgentsInWorkflows/agent.yaml
@@ -21,8 +21,8 @@ template:
     - name: AZURE_OPENAI_ENDPOINT
       value: ${AZURE_OPENAI_ENDPOINT}
     - name: AZURE_OPENAI_DEPLOYMENT_NAME
-      value: gpt-4o-mini
+      value: gpt-5.4-mini
 resources:
-  - name: "gpt-4o-mini"
+  - name: "gpt-5.4-mini"
     kind: model
-    id: gpt-4o-mini
+    id: gpt-5.4-mini
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/Program.cs b/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/Program.cs
index ca36341b97..cc1e3314f0 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/Program.cs
+++ b/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/Program.cs
@@ -13,7 +13,7 @@ using Microsoft.Agents.AI.Workflows;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT")
     ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 Console.WriteLine($"Using Azure AI endpoint: {endpoint}");
 Console.WriteLine($"Using model deployment: {deploymentName}");
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/README.md b/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/README.md
index 4f589be86e..390df95e20 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/README.md
+++ b/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/README.md
@@ -44,7 +44,7 @@ Before running this sample, ensure you have:
 
 1. **Microsoft Foundry Project**
    - Project created.
-   - Chat model deployed (e.g., `gpt-4o` or `gpt-4.1`)
+   - Chat model deployed (e.g., `gpt-5.4-mini`)
    - Note your project endpoint URL and model deployment name
      > **Note**: You can right-click the project in the Microsoft Foundry VS Code extension and select `Copy Project Endpoint URL` to get the endpoint.
 
@@ -66,14 +66,14 @@ Set the following environment variables:
 ```powershell
 # Replace with your actual values
 $env:AZURE_AI_PROJECT_ENDPOINT="https://<your-resource>.services.ai.azure.com/api/projects/<your-project>"
-$env:MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 **Bash:**
 
 ```bash
 export AZURE_AI_PROJECT_ENDPOINT="https://<your-resource>.services.ai.azure.com/api/projects/<your-project>"
-export MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+export MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ### Running the Sample
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/agent.yaml b/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/agent.yaml
index 672444cdd1..79d848fa5a 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/agent.yaml
+++ b/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/agent.yaml
@@ -24,8 +24,8 @@ template:
     - name: AZURE_AI_PROJECT_ENDPOINT
       value: ${AZURE_AI_PROJECT_ENDPOINT}
     - name: MODEL_DEPLOYMENT_NAME
-      value: gpt-4o-mini
+      value: gpt-5.4-mini
 resources:
-  - name: "gpt-4o-mini"
+  - name: "gpt-5.4-mini"
     kind: model
-    id: gpt-4o-mini
+    id: gpt-5.4-mini
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/appsettings.Development.json b/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/appsettings.Development.json
index b6b1c77b85..eae0c9ec3f 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/appsettings.Development.json
+++ b/dotnet/samples/05-end-to-end/HostedAgents/FoundryMultiAgent/appsettings.Development.json
@@ -1,4 +1,4 @@
 {
     "AZURE_AI_PROJECT_ENDPOINT": "https://<your-resource>.services.ai.azure.com/api/projects/<your-project>",
-    "MODEL_DEPLOYMENT_NAME": "gpt-4o-mini"
+    "MODEL_DEPLOYMENT_NAME": "gpt-5.4-mini"
 }
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/Program.cs b/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/Program.cs
index 185afd186f..c09a0a4a82 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/Program.cs
+++ b/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/Program.cs
@@ -19,7 +19,7 @@ using Microsoft.Extensions.AI;
 // Get configuration from environment variables
 var endpoint = Environment.GetEnvironmentVariable("AZURE_AI_PROJECT_ENDPOINT")
     ?? throw new InvalidOperationException("AZURE_AI_PROJECT_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("MODEL_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("MODEL_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 Console.WriteLine($"Project Endpoint: {endpoint}");
 Console.WriteLine($"Model Deployment: {deploymentName}");
 // Simulated hotel data for Seattle
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/README.md b/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/README.md
index e9dbced0a7..43c5a6cb69 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/README.md
+++ b/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/README.md
@@ -41,7 +41,7 @@ Before running this sample, ensure you have:
 
 1. **Microsoft Foundry Project**
    - Project created.
-   - Chat model deployed (e.g., `gpt-4o` or `gpt-4.1`)
+   - Chat model deployed (e.g., `gpt-5.4-mini`)
    - Note your project endpoint URL and model deployment name
 
 2. **Azure CLI**
@@ -58,21 +58,21 @@ Before running this sample, ensure you have:
 Set the following environment variables (matching `agent.yaml`):
 
 - `AZURE_AI_PROJECT_ENDPOINT` - Your Microsoft Foundry project endpoint URL (required)
-- `MODEL_DEPLOYMENT_NAME` - The deployment name for your chat model (defaults to `gpt-4o-mini`)
+- `MODEL_DEPLOYMENT_NAME` - The deployment name for your chat model (defaults to `gpt-5.4-mini`)
 
 **PowerShell:**
 
 ```powershell
 # Replace with your actual values
 $env:AZURE_AI_PROJECT_ENDPOINT="https://<your-resource>.services.ai.azure.com/api/projects/<your-project>"
-$env:MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+$env:MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 **Bash:**
 
 ```bash
 export AZURE_AI_PROJECT_ENDPOINT="https://<your-resource>.services.ai.azure.com/api/projects/<your-project>"
-export MODEL_DEPLOYMENT_NAME="gpt-4o-mini"
+export MODEL_DEPLOYMENT_NAME="gpt-5.4-mini"
 ```
 
 ### Running the Sample
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/agent.yaml b/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/agent.yaml
index 100defd112..eacb3ec2c0 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/agent.yaml
+++ b/dotnet/samples/05-end-to-end/HostedAgents/FoundrySingleAgent/agent.yaml
@@ -25,8 +25,8 @@ template:
     - name: AZURE_AI_PROJECT_ENDPOINT
       value: ${AZURE_AI_PROJECT_ENDPOINT}
     - name: MODEL_DEPLOYMENT_NAME
-      value: gpt-4o-mini
+      value: gpt-5.4-mini
 resources:
-  - name: "gpt-4o-mini"
+  - name: "gpt-5.4-mini"
     kind: model
-    id: gpt-4o-mini
\ No newline at end of file
+    id: gpt-5.4-mini
\ No newline at end of file
diff --git a/dotnet/samples/05-end-to-end/HostedAgents/README.md b/dotnet/samples/05-end-to-end/HostedAgents/README.md
index 2042212a2e..a2b603cc34 100644
--- a/dotnet/samples/05-end-to-end/HostedAgents/README.md
+++ b/dotnet/samples/05-end-to-end/HostedAgents/README.md
@@ -20,7 +20,7 @@ Before running any sample, ensure you have:
 
 1. **.NET 10 SDK** or later — [Download](https://dotnet.microsoft.com/download/dotnet/10.0)
 2. **Azure CLI** installed — [Install guide](https://learn.microsoft.com/cli/azure/install-azure-cli)
-3. **Azure OpenAI** or **Microsoft Foundry project** with a chat model deployed (e.g., `gpt-4o-mini`)
+3. **Azure OpenAI** or **Microsoft Foundry project** with a chat model deployed (e.g., `gpt-5.4-mini`)
 
 ### Authenticate with Azure CLI
 
@@ -38,9 +38,9 @@ Most samples require one or more of these environment variables:
 | Variable | Used By | Description |
 |----------|---------|-------------|
 | `AZURE_OPENAI_ENDPOINT` | Most samples | Your Azure OpenAI resource endpoint URL |
-| `AZURE_OPENAI_DEPLOYMENT_NAME` | Most samples | Chat model deployment name (defaults to `gpt-4o-mini`) |
+| `AZURE_OPENAI_DEPLOYMENT_NAME` | Most samples | Chat model deployment name (defaults to `gpt-5.4-mini`) |
 | `AZURE_AI_PROJECT_ENDPOINT` | AgentWithLocalTools, FoundryMultiAgent, FoundrySingleAgent | Microsoft Foundry project endpoint |
-| `MODEL_DEPLOYMENT_NAME` | AgentWithLocalTools, FoundryMultiAgent, FoundrySingleAgent | Chat model deployment name (defaults to `gpt-4o-mini`) |
+| `MODEL_DEPLOYMENT_NAME` | AgentWithLocalTools, FoundryMultiAgent, FoundrySingleAgent | Chat model deployment name (defaults to `gpt-5.4-mini`) |
 
 See each sample's README for the specific variables required.
 
diff --git a/dotnet/samples/05-end-to-end/M365Agent/README.md b/dotnet/samples/05-end-to-end/M365Agent/README.md
index 08e1c3d6c2..9bf1aa6773 100644
--- a/dotnet/samples/05-end-to-end/M365Agent/README.md
+++ b/dotnet/samples/05-end-to-end/M365Agent/README.md
@@ -4,7 +4,7 @@ This is a sample of a simple Weather Forecast Agent that is hosted on an Asp.Net
 
 This Agent Sample is intended to introduce you the basics of integrating Agent Framework with the Microsoft 365 Agents SDK in order to use Agent Framework agents in various M365 services and applications. It can also be used as the base for a custom Agent that you choose to develop.
 
-***Note:*** This sample requires JSON structured output from the model which works best from newer versions of the model such as gpt-4o-mini.
+***Note:*** This sample requires JSON structured output from the model which works best from newer versions of the model such as gpt-5.4-mini.
 
 ## Prerequisites
 
@@ -12,7 +12,7 @@ This Agent Sample is intended to introduce you the basics of integrating Agent F
 - [devtunnel](https://learn.microsoft.com/azure/developer/dev-tunnels/get-started?tabs=windows)
 - [Microsoft 365 Agents Toolkit](https://github.com/OfficeDev/microsoft-365-agents-toolkit)
 
-- You will need an Azure OpenAI or OpenAI resource using `gpt-4o-mini`
+- You will need an Azure OpenAI or OpenAI resource using `gpt-5.4-mini`
  
 - Configure OpenAI in appsettings
 
diff --git a/dotnet/samples/AGENTS.md b/dotnet/samples/AGENTS.md
index 7208facf36..89e1359e85 100644
--- a/dotnet/samples/AGENTS.md
+++ b/dotnet/samples/AGENTS.md
@@ -85,7 +85,7 @@ using OpenAI.Chat;
 
 var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT")
     ?? throw new InvalidOperationException("AZURE_OPENAI_ENDPOINT is not set.");
-var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";
+var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-5.4-mini";
 
 // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
 // In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid
@@ -97,7 +97,7 @@ AIAgent agent = new AzureOpenAIClient(new Uri(endpoint), new DefaultAzureCredent
 
 Environment variables:
 - `AZURE_OPENAI_ENDPOINT` — Your Azure OpenAI endpoint
-- `AZURE_OPENAI_DEPLOYMENT_NAME` — Model deployment name (defaults to `gpt-4o-mini`)
+- `AZURE_OPENAI_DEPLOYMENT_NAME` — Model deployment name (defaults to `gpt-5.4-mini`)
 
 For authentication, run `az login` before running samples.