diff --git a/python/packages/azure/agent_framework_azure/_assistants_client.py b/python/packages/azure/agent_framework_azure/_assistants_client.py
index 796ceba330..6c5bc6a2f2 100644
--- a/python/packages/azure/agent_framework_azure/_assistants_client.py
+++ b/python/packages/azure/agent_framework_azure/_assistants_client.py
@@ -86,7 +86,10 @@ class AzureAssistantsClient(OpenAIAssistantsClient):
             raise ServiceInitializationError("Failed to create Azure OpenAI settings.", ex) from ex
 
         if not azure_openai_settings.chat_deployment_name:
-            raise ServiceInitializationError("The Azure OpenAI deployment name is required.")
+            raise ServiceInitializationError(
+                "Azure OpenAI deployment name is required. Set via 'deployment_name' parameter "
+                "or 'AZURE_OPENAI_CHAT_DEPLOYMENT_NAME' environment variable."
+            )
 
         # Handle authentication: try API key first, then AD token, then Entra ID
         if (
diff --git a/python/packages/azure/agent_framework_azure/_chat_client.py b/python/packages/azure/agent_framework_azure/_chat_client.py
index be87b9626c..9213b40871 100644
--- a/python/packages/azure/agent_framework_azure/_chat_client.py
+++ b/python/packages/azure/agent_framework_azure/_chat_client.py
@@ -98,15 +98,16 @@ class AzureChatClient(AzureOpenAIConfigBase, OpenAIChatClientBase):
             raise ServiceInitializationError(f"Failed to validate settings: {exc}") from exc
 
         if not azure_openai_settings.chat_deployment_name:
-            raise ServiceInitializationError("chat_deployment_name is required.")
-        if not azure_openai_settings.api_version:
-            raise ServiceInitializationError("api_version is required.")
+            raise ServiceInitializationError(
+                "Azure OpenAI deployment name is required. Set via 'deployment_name' parameter "
+                "or 'AZURE_OPENAI_CHAT_DEPLOYMENT_NAME' environment variable."
+            )
 
         super().__init__(
             deployment_name=azure_openai_settings.chat_deployment_name,
             endpoint=azure_openai_settings.endpoint,
             base_url=azure_openai_settings.base_url,
-            api_version=azure_openai_settings.api_version,
+            api_version=azure_openai_settings.api_version,  # type: ignore
             api_key=azure_openai_settings.api_key.get_secret_value() if azure_openai_settings.api_key else None,
             ad_token=ad_token,
             ad_token_provider=ad_token_provider,
diff --git a/python/packages/azure/agent_framework_azure/_responses_client.py b/python/packages/azure/agent_framework_azure/_responses_client.py
index 4131a1153b..80f581f678 100644
--- a/python/packages/azure/agent_framework_azure/_responses_client.py
+++ b/python/packages/azure/agent_framework_azure/_responses_client.py
@@ -94,15 +94,16 @@ class AzureResponsesClient(AzureOpenAIConfigBase, OpenAIResponsesClientBase):
             raise ServiceInitializationError(f"Failed to validate settings: {exc}") from exc
 
         if not azure_openai_settings.responses_deployment_name:
-            raise ServiceInitializationError("responses_deployment_name is required.")
-        if not azure_openai_settings.api_version:
-            raise ServiceInitializationError("api_version is required.")
+            raise ServiceInitializationError(
+                "Azure OpenAI deployment name is required. Set via 'deployment_name' parameter "
+                "or 'AZURE_OPENAI_RESPONSES_DEPLOYMENT_NAME' environment variable."
+            )
 
         super().__init__(
             deployment_name=azure_openai_settings.responses_deployment_name,
             endpoint=azure_openai_settings.endpoint,
             base_url=azure_openai_settings.base_url,
-            api_version=azure_openai_settings.api_version,
+            api_version=azure_openai_settings.api_version,  # type: ignore
             api_key=azure_openai_settings.api_key.get_secret_value() if azure_openai_settings.api_key else None,
             ad_token=ad_token,
             ad_token_provider=ad_token_provider,
diff --git a/python/packages/foundry/agent_framework_foundry/_chat_client.py b/python/packages/foundry/agent_framework_foundry/_chat_client.py
index a3e55be440..b6129a0d42 100644
--- a/python/packages/foundry/agent_framework_foundry/_chat_client.py
+++ b/python/packages/foundry/agent_framework_foundry/_chat_client.py
@@ -157,14 +157,20 @@ class FoundryChatClient(ChatClientBase):
         should_close_client = False
         if client is None:
             if not foundry_settings.project_endpoint:
-                raise ServiceInitializationError("Project endpoint is required when client is not provided.")
+                raise ServiceInitializationError(
+                    "Foundry project endpoint is required. Set via 'project_endpoint' parameter "
+                    "or 'FOUNDRY_PROJECT_ENDPOINT' environment variable."
+                )
 
             if agent_id is None and not foundry_settings.model_deployment_name:
-                raise ServiceInitializationError("Model deployment name is required for agent creation.")
+                raise ServiceInitializationError(
+                    "Foundry model deployment name is required. Set via 'model_deployment_name' parameter "
+                    "or 'FOUNDRY_MODEL_DEPLOYMENT_NAME' environment variable."
+                )
 
             # Use provided credential
             if not async_credential:
-                raise ServiceInitializationError("Azure AD credential is required when client is not provided.")
+                raise ServiceInitializationError("Azure credential is required when client is not provided.")
             client = AIProjectClient(endpoint=foundry_settings.project_endpoint, credential=async_credential)
             should_close_client = True
 
diff --git a/python/packages/foundry/tests/test_foundry_chat_client.py b/python/packages/foundry/tests/test_foundry_chat_client.py
index fa69707110..d88bcbb4ac 100644
--- a/python/packages/foundry/tests/test_foundry_chat_client.py
+++ b/python/packages/foundry/tests/test_foundry_chat_client.py
@@ -131,9 +131,7 @@ def test_foundry_chat_client_init_missing_project_endpoint() -> None:
         mock_settings_instance.agent_name = "test-agent"
         mock_settings.return_value = mock_settings_instance
 
-        with pytest.raises(
-            ServiceInitializationError, match="Project endpoint is required when client is not provided"
-        ):
+        with pytest.raises(ServiceInitializationError, match="project endpoint is required"):
             FoundryChatClient(
                 client=None,
                 agent_id=None,
@@ -153,7 +151,7 @@ def test_foundry_chat_client_init_missing_model_deployment_for_agent_creation()
         mock_settings_instance.agent_name = "test-agent"
         mock_settings.return_value = mock_settings_instance
 
-        with pytest.raises(ServiceInitializationError, match="Model deployment name is required for agent creation"):
+        with pytest.raises(ServiceInitializationError, match="model deployment name is required"):
             FoundryChatClient(
                 client=None,
                 agent_id=None,  # No existing agent
@@ -194,7 +192,7 @@ def test_foundry_chat_client_from_dict(mock_ai_project_client: MagicMock) -> Non
 
 def test_foundry_chat_client_init_missing_credential(foundry_unit_test_env: dict[str, str]) -> None:
     """Test FoundryChatClient.__init__ when async_credential is missing and no client provided."""
-    with pytest.raises(ServiceInitializationError, match="Azure AD credential is required when client is not provided"):
+    with pytest.raises(ServiceInitializationError, match="Azure credential is required when client is not provided"):
         FoundryChatClient(
             client=None,
             agent_id="existing-agent",
diff --git a/python/packages/main/agent_framework/openai/_assistants_client.py b/python/packages/main/agent_framework/openai/_assistants_client.py
index 2cde074875..6bd1857b27 100644
--- a/python/packages/main/agent_framework/openai/_assistants_client.py
+++ b/python/packages/main/agent_framework/openai/_assistants_client.py
@@ -107,9 +107,14 @@ class OpenAIAssistantsClient(OpenAIConfigBase, ChatClientBase):
             raise ServiceInitializationError("Failed to create OpenAI settings.", ex) from ex
 
         if not async_client and not openai_settings.api_key:
-            raise ServiceInitializationError("The OpenAI API key is required.")
+            raise ServiceInitializationError(
+                "OpenAI API key is required. Set via 'api_key' parameter or 'OPENAI_API_KEY' environment variable."
+            )
         if not openai_settings.chat_model_id:
-            raise ServiceInitializationError("The OpenAI model ID is required.")
+            raise ServiceInitializationError(
+                "OpenAI model ID is required. "
+                "Set via 'ai_model_id' parameter or 'OPENAI_CHAT_MODEL_ID' environment variable."
+            )
 
         super().__init__(
             ai_model_id=openai_settings.chat_model_id,
diff --git a/python/packages/main/agent_framework/openai/_chat_client.py b/python/packages/main/agent_framework/openai/_chat_client.py
index 12546ab1e3..a242ccf364 100644
--- a/python/packages/main/agent_framework/openai/_chat_client.py
+++ b/python/packages/main/agent_framework/openai/_chat_client.py
@@ -417,9 +417,14 @@ class OpenAIChatClient(OpenAIConfigBase, OpenAIChatClientBase):
             raise ServiceInitializationError("Failed to create OpenAI settings.", ex) from ex
 
         if not async_client and not openai_settings.api_key:
-            raise ServiceInitializationError("The OpenAI API key is required.")
+            raise ServiceInitializationError(
+                "OpenAI API key is required. Set via 'api_key' parameter or 'OPENAI_API_KEY' environment variable."
+            )
         if not openai_settings.chat_model_id:
-            raise ServiceInitializationError("The OpenAI model ID is required.")
+            raise ServiceInitializationError(
+                "OpenAI model ID is required. "
+                "Set via 'ai_model_id' parameter or 'OPENAI_CHAT_MODEL_ID' environment variable."
+            )
 
         super().__init__(
             ai_model_id=openai_settings.chat_model_id,
diff --git a/python/packages/main/agent_framework/openai/_responses_client.py b/python/packages/main/agent_framework/openai/_responses_client.py
index a6ae718e42..015c687eb4 100644
--- a/python/packages/main/agent_framework/openai/_responses_client.py
+++ b/python/packages/main/agent_framework/openai/_responses_client.py
@@ -862,9 +862,14 @@ class OpenAIResponsesClient(OpenAIConfigBase, OpenAIResponsesClientBase):
             raise ServiceInitializationError("Failed to create OpenAI settings.", ex) from ex
 
         if not async_client and not openai_settings.api_key:
-            raise ServiceInitializationError("The OpenAI API key is required.")
+            raise ServiceInitializationError(
+                "OpenAI API key is required. Set via 'api_key' parameter or 'OPENAI_API_KEY' environment variable."
+            )
         if not openai_settings.responses_model_id:
-            raise ServiceInitializationError("The OpenAI model ID is required.")
+            raise ServiceInitializationError(
+                "OpenAI model ID is required. "
+                "Set via 'ai_model_id' parameter or 'OPENAI_RESPONSES_MODEL_ID' environment variable."
+            )
 
         super().__init__(
             ai_model_id=openai_settings.responses_model_id,