diff --git a/dotnet/src/Microsoft.Agents.AI.Abstractions/AgentAbstractionsJsonUtilities.cs b/dotnet/src/Microsoft.Agents.AI.Abstractions/AgentAbstractionsJsonUtilities.cs
index 8943e29c79..d5003cace0 100644
--- a/dotnet/src/Microsoft.Agents.AI.Abstractions/AgentAbstractionsJsonUtilities.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Abstractions/AgentAbstractionsJsonUtilities.cs
@@ -50,12 +50,16 @@ public static partial class AgentAbstractionsJsonUtilities
             Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping, // same as AIJsonUtilities
         };
 
-        // Chain with all supported types from Microsoft.Extensions.AI.Abstractions.
+        // Chain in the resolvers from both AIJsonUtilities and our source generated context.
+        // We want AIJsonUtilities first to ensure any M.E.AI types are handled via its resolver.
+        options.TypeInfoResolverChain.Clear();
+        options.TypeInfoResolverChain.Add(AIJsonUtilities.DefaultOptions.TypeInfoResolver!);
+        options.TypeInfoResolverChain.Add(JsonContext.Default.Options.TypeInfoResolver!);
+
         // If reflection-based serialization is enabled by default, this includes
         // the default type info resolver that utilizes reflection, but we need to manually
         // apply the same converter AIJsonUtilities adds for string-based enum serialization,
         // as that's not propagated as part of the resolver.
-        options.TypeInfoResolverChain.Add(AIJsonUtilities.DefaultOptions.TypeInfoResolver!);
         if (JsonSerializer.IsReflectionEnabledByDefault)
         {
             options.Converters.Add(new JsonStringEnumConverter());
diff --git a/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/ChatCompletions/ChatCompletionsJsonSerializerOptions.cs b/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/ChatCompletions/ChatCompletionsJsonSerializerOptions.cs
index b009b82d29..301cae1f8f 100644
--- a/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/ChatCompletions/ChatCompletionsJsonSerializerOptions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/ChatCompletions/ChatCompletionsJsonSerializerOptions.cs
@@ -17,7 +17,13 @@ internal static class ChatCompletionsJsonSerializerOptions
     private static JsonSerializerOptions Create()
     {
         JsonSerializerOptions options = new(ChatCompletionsJsonContext.Default.Options);
+
+        // Chain in the resolvers from both AgentAbstractionsJsonUtilities and our source generated context.
+        // We want AgentAbstractionsJsonUtilities first to ensure any M.E.AI types are handled via its resolver.
+        options.TypeInfoResolverChain.Clear();
         options.TypeInfoResolverChain.Add(AgentAbstractionsJsonUtilities.DefaultOptions.TypeInfoResolver!);
+        options.TypeInfoResolverChain.Add(ChatCompletionsJsonContext.Default.Options.TypeInfoResolver!);
+
         options.MakeReadOnly();
         return options;
     }
diff --git a/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/OpenAIHostingJsonUtilities.cs b/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/OpenAIHostingJsonUtilities.cs
index ceac8b872f..49ceef622a 100644
--- a/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/OpenAIHostingJsonUtilities.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/OpenAIHostingJsonUtilities.cs
@@ -24,7 +24,13 @@ internal static class OpenAIHostingJsonUtilities
     private static JsonSerializerOptions CreateDefaultOptions()
     {
         JsonSerializerOptions options = new(OpenAIHostingJsonContext.Default.Options);
+
+        // Chain in the resolvers from both AgentAbstractionsJsonUtilities and our source generated context.
+        // We want AgentAbstractionsJsonUtilities first to ensure any M.E.AI types are handled via its resolver.
+        options.TypeInfoResolverChain.Clear();
         options.TypeInfoResolverChain.Add(AgentAbstractionsJsonUtilities.DefaultOptions.TypeInfoResolver!);
+        options.TypeInfoResolverChain.Add(OpenAIHostingJsonContext.Default.Options.TypeInfoResolver!);
+
         options.MakeReadOnly();
         return options;
     }
diff --git a/dotnet/src/Microsoft.Agents.AI.Mem0/Mem0JsonUtilities.cs b/dotnet/src/Microsoft.Agents.AI.Mem0/Mem0JsonUtilities.cs
index eb50d31f70..d139cb0f76 100644
--- a/dotnet/src/Microsoft.Agents.AI.Mem0/Mem0JsonUtilities.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Mem0/Mem0JsonUtilities.cs
@@ -4,7 +4,6 @@ using System.Diagnostics.CodeAnalysis;
 using System.Text.Encodings.Web;
 using System.Text.Json;
 using System.Text.Json.Serialization;
-using Microsoft.Extensions.AI;
 
 namespace Microsoft.Agents.AI.Mem0;
 
@@ -44,8 +43,12 @@ public static partial class Mem0JsonUtilities
             Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping, // same as in AIJsonUtilities
         };
 
-        // Chain with all supported types from Microsoft.Extensions.AI.Abstractions.
-        options.TypeInfoResolverChain.Add(AIJsonUtilities.DefaultOptions.TypeInfoResolver!);
+        // Chain in the resolvers from both AgentAbstractionsJsonUtilities and our source generated context.
+        // We want AgentAbstractionsJsonUtilities first to ensure any M.E.AI types are handled via its resolver.
+        options.TypeInfoResolverChain.Clear();
+        options.TypeInfoResolverChain.Add(AgentAbstractionsJsonUtilities.DefaultOptions.TypeInfoResolver!);
+        options.TypeInfoResolverChain.Add(JsonContext.Default.Options.TypeInfoResolver!);
+
         if (JsonSerializer.IsReflectionEnabledByDefault)
         {
             options.Converters.Add(new JsonStringEnumConverter());
diff --git a/dotnet/src/Microsoft.Agents.AI/AgentJsonUtilities.cs b/dotnet/src/Microsoft.Agents.AI/AgentJsonUtilities.cs
index 5ef6978c00..36bef4a2af 100644
--- a/dotnet/src/Microsoft.Agents.AI/AgentJsonUtilities.cs
+++ b/dotnet/src/Microsoft.Agents.AI/AgentJsonUtilities.cs
@@ -44,8 +44,12 @@ internal static partial class AgentJsonUtilities
             Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping, // same as in AgentAbstractionsJsonUtilities and AIJsonUtilities
         };
 
-        // Chain with all supported types from Microsoft.Agents.AI.Abstractions.
+        // Chain in the resolvers from both AgentAbstractionsJsonUtilities and our source generated context.
+        // We want AgentAbstractionsJsonUtilities first to ensure any M.E.AI types are handled via its resolver.
+        options.TypeInfoResolverChain.Clear();
         options.TypeInfoResolverChain.Add(AgentAbstractionsJsonUtilities.DefaultOptions.TypeInfoResolver!);
+        options.TypeInfoResolverChain.Add(JsonContext.Default.Options.TypeInfoResolver!);
+
         if (JsonSerializer.IsReflectionEnabledByDefault)
         {
             options.Converters.Add(new JsonStringEnumConverter());
diff --git a/dotnet/tests/Microsoft.Agents.AI.Abstractions.UnitTests/InMemoryChatMessageStoreTests.cs b/dotnet/tests/Microsoft.Agents.AI.Abstractions.UnitTests/InMemoryChatMessageStoreTests.cs
index fedd0ce591..4c793d17f4 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Abstractions.UnitTests/InMemoryChatMessageStoreTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Abstractions.UnitTests/InMemoryChatMessageStoreTests.cs
@@ -114,6 +114,23 @@ public class InMemoryChatMessageStoreTests
         Assert.Equal("B", newStore[1].Text);
     }
 
+    [Fact]
+    public async Task SerializeAndDeserializeWorksWithExperimentalContentTypesAsync()
+    {
+        var store = new InMemoryChatMessageStore
+        {
+            new ChatMessage(ChatRole.User, [new FunctionApprovalRequestContent("call123", new FunctionCallContent("call123", "some_func"))]),
+            new ChatMessage(ChatRole.Assistant, [new FunctionApprovalResponseContent("call123", true, new FunctionCallContent("call123", "some_func"))])
+        };
+
+        var jsonElement = store.Serialize();
+        var newStore = new InMemoryChatMessageStore(jsonElement);
+
+        Assert.Equal(2, newStore.Count);
+        Assert.IsType<FunctionApprovalRequestContent>(newStore[0].Contents[0]);
+        Assert.IsType<FunctionApprovalResponseContent>(newStore[1].Contents[0]);
+    }
+
     [Fact]
     public async Task AddMessagesAsyncWithEmptyMessagesDoesNotChangeStoreAsync()
     {