diff --git a/dotnet/src/Microsoft.Agents.AI.GitHub.Copilot/GitHubCopilotAgent.cs b/dotnet/src/Microsoft.Agents.AI.GitHub.Copilot/GitHubCopilotAgent.cs
index b584ce7983..11b0dbc62b 100644
--- a/dotnet/src/Microsoft.Agents.AI.GitHub.Copilot/GitHubCopilotAgent.cs
+++ b/dotnet/src/Microsoft.Agents.AI.GitHub.Copilot/GitHubCopilotAgent.cs
@@ -333,6 +333,8 @@ internal static ResumeSessionConfig CopyResumeSessionConfig(SessionConfig? sourc
         {
             Model = source?.Model,
             ReasoningEffort = source?.ReasoningEffort,
+            ReasoningSummary = source?.ReasoningSummary,
+            ContextTier = source?.ContextTier,
             Tools = source?.Tools,
             SystemMessage = source?.SystemMessage,
             AvailableTools = source?.AvailableTools,
diff --git a/dotnet/tests/Microsoft.Agents.AI.GitHub.Copilot.UnitTests/GitHubCopilotAgentTests.cs b/dotnet/tests/Microsoft.Agents.AI.GitHub.Copilot.UnitTests/GitHubCopilotAgentTests.cs
index 25316d4705..fc073b7b69 100644
--- a/dotnet/tests/Microsoft.Agents.AI.GitHub.Copilot.UnitTests/GitHubCopilotAgentTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.GitHub.Copilot.UnitTests/GitHubCopilotAgentTests.cs
@@ -169,6 +169,8 @@ public void CopyResumeSessionConfig_CopiesAllProperties()
         {
             Model = "gpt-4o",
             ReasoningEffort = "high",
+            ReasoningSummary = ReasoningSummary.Detailed,
+            ContextTier = ContextTier.LongContext,
             Tools = tools,
             SystemMessage = systemMessage,
             AvailableTools = ["tool1", "tool2"],
@@ -189,6 +191,8 @@ public void CopyResumeSessionConfig_CopiesAllProperties()
         // Assert
         Assert.Equal("gpt-4o", result.Model);
         Assert.Equal("high", result.ReasoningEffort);
+        Assert.Equal(ReasoningSummary.Detailed, result.ReasoningSummary);
+        Assert.Equal(ContextTier.LongContext, result.ContextTier);
         Assert.Same(tools, result.Tools);
         Assert.Same(systemMessage, result.SystemMessage);
         Assert.Equal(["tool1", "tool2"], result.AvailableTools);
@@ -213,6 +217,8 @@ public void CopyResumeSessionConfig_WithNullSource_ReturnsDefaults()
         // Assert
         Assert.Null(result.Model);
         Assert.Null(result.ReasoningEffort);
+        Assert.Null(result.ReasoningSummary);
+        Assert.Null(result.ContextTier);
         Assert.Null(result.Tools);
         Assert.Null(result.SystemMessage);
         Assert.Null(result.OnPermissionRequest);
@@ -223,6 +229,26 @@ public void CopyResumeSessionConfig_WithNullSource_ReturnsDefaults()
         Assert.True(result.Streaming);
     }
 
+    [Fact]
+    public void CopyResumeSessionConfig_RoundTripsReasoningSummary()
+    {
+        // Regression: ReasoningSummary controls whether the model returns readable
+        // extended-thinking summaries. It must round-trip onto resumed turns, just like
+        // ReasoningEffort, otherwise callers lose readable reasoning after the first turn.
+        var source = new SessionConfig
+        {
+            ReasoningEffort = "high",
+            ReasoningSummary = ReasoningSummary.Detailed,
+        };
+
+        // Act
+        ResumeSessionConfig result = GitHubCopilotAgent.CopyResumeSessionConfig(source);
+
+        // Assert
+        Assert.Equal(ReasoningSummary.Detailed, result.ReasoningSummary);
+        Assert.Equal("high", result.ReasoningEffort);
+    }
+
     [Fact]
     public void CopySessionConfig_WithStreamingDisabled_PreservesStreamingValue()
     {