diff --git a/dotnet/src/Microsoft.Agents.AI.OpenAI/Extensions/OpenAIResponseClientExtensions.cs b/dotnet/src/Microsoft.Agents.AI.OpenAI/Extensions/OpenAIResponseClientExtensions.cs
index 4ceff757431..642c0da2034 100644
--- a/dotnet/src/Microsoft.Agents.AI.OpenAI/Extensions/OpenAIResponseClientExtensions.cs
+++ b/dotnet/src/Microsoft.Agents.AI.OpenAI/Extensions/OpenAIResponseClientExtensions.cs
@@ -120,9 +120,24 @@ public static IChatClient AsIChatClientWithStoredOutputDisabled(this ResponsesCl
         return Throw.IfNull(responseClient)
             .AsIChatClient(model)
             .AsBuilder()
-            .ConfigureOptions(x => x.RawRepresentationFactory = _ => includeReasoningEncryptedContent
-                ? new CreateResponseOptions() { StoredOutputEnabled = false, IncludedProperties = { IncludedResponseProperty.ReasoningEncryptedContent } }
-                : new CreateResponseOptions() { StoredOutputEnabled = false })
+            .ConfigureOptions(x =>
+            {
+                var previousFactory = x.RawRepresentationFactory;
+                x.RawRepresentationFactory = state =>
+                {
+                    var responseOptions = previousFactory?.Invoke(state) as CreateResponseOptions ?? new CreateResponseOptions();
+
+                    responseOptions.StoredOutputEnabled = false;
+
+                    if (includeReasoningEncryptedContent &&
+                        !responseOptions.IncludedProperties.Contains(IncludedResponseProperty.ReasoningEncryptedContent))
+                    {
+                        responseOptions.IncludedProperties.Add(IncludedResponseProperty.ReasoningEncryptedContent);
+                    }
+
+                    return responseOptions;
+                };
+            })
             .Build();
     }
 }
diff --git a/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/ProjectResponsesClientExtensionsTests.cs b/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/ProjectResponsesClientExtensionsTests.cs
index fda9962e124..b1424bb403b 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/ProjectResponsesClientExtensionsTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Foundry.UnitTests/ProjectResponsesClientExtensionsTests.cs
@@ -129,6 +129,75 @@ public void AsIChatClientWithStoredOutputDisabled_WithIncludeReasoningFalse_Conf
         Assert.DoesNotContain(IncludedResponseProperty.ReasoningEncryptedContent, createResponseOptions.IncludedProperties);
     }
 
+    /// <summary>
+    /// Verify that AsIChatClientWithStoredOutputDisabled preserves an existing RawRepresentationFactory
+    /// set on ChatOptions, augmenting it with StoredOutputEnabled and ReasoningEncryptedContent
+    /// rather than replacing it.
+    /// </summary>
+    [Fact]
+    public void AsIChatClientWithStoredOutputDisabled_PreservesExistingRawRepresentationFactory()
+    {
+        // Arrange
+        var responseClient = CreateTestClient();
+        var chatClient = responseClient.AsIChatClientWithStoredOutputDisabled();
+
+        // Simulate a caller setting their own RawRepresentationFactory on ChatOptions
+        // (e.g., to add WebSearchCallActionSources).
+        var options = new ChatOptions
+        {
+            RawRepresentationFactory = _ => new CreateResponseOptions
+            {
+                IncludedProperties = { IncludedResponseProperty.WebSearchCallActionSources },
+            },
+        };
+
+        // Act
+        var createResponseOptions = GetCreateResponseOptionsFromPipeline(chatClient, options);
+
+        // Assert
+        Assert.NotNull(createResponseOptions);
+        Assert.False(createResponseOptions.StoredOutputEnabled);
+        Assert.Contains(IncludedResponseProperty.ReasoningEncryptedContent, createResponseOptions.IncludedProperties);
+        Assert.Contains(IncludedResponseProperty.WebSearchCallActionSources, createResponseOptions.IncludedProperties);
+    }
+
+    /// <summary>
+    /// Verify that AsIChatClientWithStoredOutputDisabled does not duplicate ReasoningEncryptedContent
+    /// when the existing factory already includes it.
+    /// </summary>
+    [Fact]
+    public void AsIChatClientWithStoredOutputDisabled_DoesNotDuplicateReasoningEncryptedContent()
+    {
+        // Arrange
+        var responseClient = CreateTestClient();
+        var chatClient = responseClient.AsIChatClientWithStoredOutputDisabled();
+
+        // Simulate a caller that already includes ReasoningEncryptedContent
+        var options = new ChatOptions
+        {
+            RawRepresentationFactory = _ => new CreateResponseOptions
+            {
+                IncludedProperties = { IncludedResponseProperty.ReasoningEncryptedContent },
+            },
+        };
+
+        // Act
+        var createResponseOptions = GetCreateResponseOptionsFromPipeline(chatClient, options);
+
+        // Assert - ReasoningEncryptedContent should appear exactly once
+        Assert.NotNull(createResponseOptions);
+        int count = 0;
+        foreach (var prop in createResponseOptions.IncludedProperties)
+        {
+            if (prop == IncludedResponseProperty.ReasoningEncryptedContent)
+            {
+                count++;
+            }
+        }
+
+        Assert.Equal(1, count);
+    }
+
     /// <summary>
     /// Verify that AsIChatClientWithStoredOutputDisabled works with an optional deployment name.
     /// </summary>
@@ -153,6 +222,15 @@ public void AsIChatClientWithStoredOutputDisabled_WithDeploymentName_ConfiguresS
     /// by using reflection to access the configure action and invoking it on a test <see cref="ChatOptions"/>.
     /// </summary>
     private static CreateResponseOptions? GetCreateResponseOptionsFromPipeline(IChatClient chatClient)
+    {
+        return GetCreateResponseOptionsFromPipeline(chatClient, new ChatOptions());
+    }
+
+    /// <summary>
+    /// Overload that runs the configure action on caller-supplied <see cref="ChatOptions"/>,
+    /// useful for testing that existing factories are preserved.
+    /// </summary>
+    private static CreateResponseOptions? GetCreateResponseOptionsFromPipeline(IChatClient chatClient, ChatOptions options)
     {
         var configureField = chatClient.GetType().GetField("_configureOptions", BindingFlags.NonPublic | BindingFlags.Instance);
         Assert.NotNull(configureField);
@@ -160,7 +238,6 @@ public void AsIChatClientWithStoredOutputDisabled_WithDeploymentName_ConfiguresS
         var configureAction = configureField.GetValue(chatClient) as Action<ChatOptions>;
         Assert.NotNull(configureAction);
 
-        var options = new ChatOptions();
         configureAction(options);
 
         Assert.NotNull(options.RawRepresentationFactory);
diff --git a/dotnet/tests/Microsoft.Agents.AI.OpenAI.UnitTests/Extensions/OpenAIResponseClientExtensionsTests.cs b/dotnet/tests/Microsoft.Agents.AI.OpenAI.UnitTests/Extensions/OpenAIResponseClientExtensionsTests.cs
index 1205889e199..eede6ec6375 100644
--- a/dotnet/tests/Microsoft.Agents.AI.OpenAI.UnitTests/Extensions/OpenAIResponseClientExtensionsTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.OpenAI.UnitTests/Extensions/OpenAIResponseClientExtensionsTests.cs
@@ -370,6 +370,75 @@ public void AsIChatClientWithStoredOutputDisabled_WithIncludeReasoningFalse_Conf
         Assert.DoesNotContain(IncludedResponseProperty.ReasoningEncryptedContent, createResponseOptions.IncludedProperties);
     }
 
+    /// <summary>
+    /// Verify that AsIChatClientWithStoredOutputDisabled preserves an existing RawRepresentationFactory
+    /// set on ChatOptions, augmenting it with StoredOutputEnabled and ReasoningEncryptedContent
+    /// rather than replacing it.
+    /// </summary>
+    [Fact]
+    public void AsIChatClientWithStoredOutputDisabled_PreservesExistingRawRepresentationFactory()
+    {
+        // Arrange
+        var responseClient = new TestOpenAIResponseClient();
+        var chatClient = responseClient.AsIChatClientWithStoredOutputDisabled();
+
+        // Simulate a caller setting their own RawRepresentationFactory on ChatOptions
+        // (e.g., to add WebSearchCallActionSources).
+        var options = new ChatOptions
+        {
+            RawRepresentationFactory = _ => new CreateResponseOptions
+            {
+                IncludedProperties = { IncludedResponseProperty.WebSearchCallActionSources },
+            },
+        };
+
+        // Act
+        var createResponseOptions = GetCreateResponseOptionsFromPipeline(chatClient, options);
+
+        // Assert
+        Assert.NotNull(createResponseOptions);
+        Assert.False(createResponseOptions.StoredOutputEnabled);
+        Assert.Contains(IncludedResponseProperty.ReasoningEncryptedContent, createResponseOptions.IncludedProperties);
+        Assert.Contains(IncludedResponseProperty.WebSearchCallActionSources, createResponseOptions.IncludedProperties);
+    }
+
+    /// <summary>
+    /// Verify that AsIChatClientWithStoredOutputDisabled does not duplicate ReasoningEncryptedContent
+    /// when the existing factory already includes it.
+    /// </summary>
+    [Fact]
+    public void AsIChatClientWithStoredOutputDisabled_DoesNotDuplicateReasoningEncryptedContent()
+    {
+        // Arrange
+        var responseClient = new TestOpenAIResponseClient();
+        var chatClient = responseClient.AsIChatClientWithStoredOutputDisabled();
+
+        // Simulate a caller that already includes ReasoningEncryptedContent
+        var options = new ChatOptions
+        {
+            RawRepresentationFactory = _ => new CreateResponseOptions
+            {
+                IncludedProperties = { IncludedResponseProperty.ReasoningEncryptedContent },
+            },
+        };
+
+        // Act
+        var createResponseOptions = GetCreateResponseOptionsFromPipeline(chatClient, options);
+
+        // Assert - ReasoningEncryptedContent should appear exactly once
+        Assert.NotNull(createResponseOptions);
+        int count = 0;
+        foreach (var prop in createResponseOptions.IncludedProperties)
+        {
+            if (prop == IncludedResponseProperty.ReasoningEncryptedContent)
+            {
+                count++;
+            }
+        }
+
+        Assert.Equal(1, count);
+    }
+
     /// <summary>
     /// A simple test IServiceProvider implementation for testing.
     /// </summary>
@@ -394,6 +463,15 @@ private sealed class TestServiceProvider : IServiceProvider
     /// by using reflection to access the configure action and invoking it on a test <see cref="ChatOptions"/>.
     /// </summary>
     private static CreateResponseOptions? GetCreateResponseOptionsFromPipeline(IChatClient chatClient)
+    {
+        return GetCreateResponseOptionsFromPipeline(chatClient, new ChatOptions());
+    }
+
+    /// <summary>
+    /// Overload that runs the configure action on caller-supplied <see cref="ChatOptions"/>,
+    /// useful for testing that existing factories are preserved.
+    /// </summary>
+    private static CreateResponseOptions? GetCreateResponseOptionsFromPipeline(IChatClient chatClient, ChatOptions options)
     {
         // The ConfigureOptionsChatClient stores the configure action in a private field.
         var configureField = chatClient.GetType().GetField("_configureOptions", BindingFlags.NonPublic | BindingFlags.Instance);
@@ -402,7 +480,6 @@ private sealed class TestServiceProvider : IServiceProvider
         var configureAction = configureField.GetValue(chatClient) as Action<ChatOptions>;
         Assert.NotNull(configureAction);
 
-        var options = new ChatOptions();
         configureAction(options);
 
         Assert.NotNull(options.RawRepresentationFactory);