diff --git a/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs b/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs
index 44a136da3e..e59ec698b8 100644
--- a/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs
+++ b/dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs
@@ -549,6 +549,7 @@ internal async Task NotifyProvidersOfFailureAsync(
         requestChatOptions.ModelId ??= this._agentOptions.ChatOptions.ModelId;
         requestChatOptions.PresencePenalty ??= this._agentOptions.ChatOptions.PresencePenalty;
         requestChatOptions.ResponseFormat ??= this._agentOptions.ChatOptions.ResponseFormat;
+        requestChatOptions.Reasoning ??= this._agentOptions.ChatOptions.Reasoning;
         requestChatOptions.Seed ??= this._agentOptions.ChatOptions.Seed;
         requestChatOptions.Temperature ??= this._agentOptions.ChatOptions.Temperature;
         requestChatOptions.TopP ??= this._agentOptions.ChatOptions.TopP;
diff --git a/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgent_ChatOptionsMergingTests.cs b/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgent_ChatOptionsMergingTests.cs
index e4df863ce0..c4766b83f0 100644
--- a/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgent_ChatOptionsMergingTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgent_ChatOptionsMergingTests.cs
@@ -347,6 +347,115 @@ public async Task ChatOptionsMergingUsesRawRepresentationFactoryWithFallbackAsyn
         Assert.Equal(expectedSetting, capturedChatOptions.RawRepresentationFactory(null!));
     }
 
+    /// <summary>
+    /// Verify that <see cref="ChatOptions.Reasoning"/> from the request takes priority over the agent's.
+    /// </summary>
+    [Fact]
+    public async Task ChatOptionsMergingUsesRequestReasoningOverAgentReasoningAsync()
+    {
+        // Arrange
+        var agentReasoning = new ReasoningOptions { Effort = ReasoningEffort.Low, Output = ReasoningOutput.Full };
+        var requestReasoning = new ReasoningOptions { Effort = ReasoningEffort.High, Output = ReasoningOutput.Full };
+
+        Mock<IChatClient> mockService = new();
+        ChatOptions? capturedChatOptions = null;
+        mockService.Setup(
+            s => s.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .Callback<IEnumerable<ChatMessage>, ChatOptions, CancellationToken>((msgs, opts, ct) =>
+                capturedChatOptions = opts)
+            .ReturnsAsync(new ChatResponse([new(ChatRole.Assistant, "response")]));
+
+        ChatClientAgent agent = new(mockService.Object, options: new()
+        {
+            ChatOptions = new ChatOptions { Reasoning = agentReasoning }
+        });
+        var messages = new List<ChatMessage> { new(ChatRole.User, "test") };
+
+        // Act
+        await agent.RunAsync(messages, options: new ChatClientAgentRunOptions(new ChatOptions { Reasoning = requestReasoning }));
+
+        // Assert
+        Assert.NotNull(capturedChatOptions);
+        Assert.NotNull(capturedChatOptions.Reasoning);
+        Assert.Equal(requestReasoning.Effort, capturedChatOptions.Reasoning.Effort);
+        Assert.Equal(requestReasoning.Output, capturedChatOptions.Reasoning.Output);
+    }
+
+    /// <summary>
+    /// Verify that <see cref="ChatOptions.Reasoning"/> falls back to the agent's when the request has none.
+    /// </summary>
+    [Fact]
+    public async Task ChatOptionsMergingFallsBackToAgentReasoningWhenRequestHasNoneAsync()
+    {
+        // Arrange
+        var agentReasoning = new ReasoningOptions { Effort = ReasoningEffort.Low, Output = ReasoningOutput.Full };
+
+        Mock<IChatClient> mockService = new();
+        ChatOptions? capturedChatOptions = null;
+        mockService.Setup(
+            s => s.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .Callback<IEnumerable<ChatMessage>, ChatOptions, CancellationToken>((msgs, opts, ct) =>
+                capturedChatOptions = opts)
+            .ReturnsAsync(new ChatResponse([new(ChatRole.Assistant, "response")]));
+
+        ChatClientAgent agent = new(mockService.Object, options: new()
+        {
+            ChatOptions = new ChatOptions { Reasoning = agentReasoning }
+        });
+        var messages = new List<ChatMessage> { new(ChatRole.User, "test") };
+
+        // Act
+        await agent.RunAsync(messages, options: new ChatClientAgentRunOptions(new ChatOptions()));
+
+        // Assert
+        Assert.NotNull(capturedChatOptions);
+        Assert.NotNull(capturedChatOptions.Reasoning);
+        Assert.Equal(agentReasoning.Effort, capturedChatOptions.Reasoning.Effort);
+        Assert.Equal(agentReasoning.Output, capturedChatOptions.Reasoning.Output);
+    }
+
+    /// <summary>
+    /// Verify that <see cref="ChatOptions.Reasoning"/> from the request is used when the agent has none.
+    /// </summary>
+    [Fact]
+    public async Task ChatOptionsMergingUsesRequestReasoningWhenAgentHasNoneAsync()
+    {
+        // Arrange
+        var requestReasoning = new ReasoningOptions { Effort = ReasoningEffort.High, Output = ReasoningOutput.Full };
+
+        Mock<IChatClient> mockService = new();
+        ChatOptions? capturedChatOptions = null;
+        mockService.Setup(
+            s => s.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .Callback<IEnumerable<ChatMessage>, ChatOptions, CancellationToken>((msgs, opts, ct) =>
+                capturedChatOptions = opts)
+            .ReturnsAsync(new ChatResponse([new(ChatRole.Assistant, "response")]));
+
+        ChatClientAgent agent = new(mockService.Object, options: new()
+        {
+            ChatOptions = new ChatOptions()
+        });
+        var messages = new List<ChatMessage> { new(ChatRole.User, "test") };
+
+        // Act
+        await agent.RunAsync(messages, options: new ChatClientAgentRunOptions(new ChatOptions { Reasoning = requestReasoning }));
+
+        // Assert
+        Assert.NotNull(capturedChatOptions);
+        Assert.NotNull(capturedChatOptions.Reasoning);
+        Assert.Equal(requestReasoning.Effort, capturedChatOptions.Reasoning.Effort);
+        Assert.Equal(requestReasoning.Output, capturedChatOptions.Reasoning.Output);
+    }
+
     /// <summary>
     /// Verify that ChatOptions merging handles all scalar properties correctly.
     /// </summary>