.NET: fix: preserve Responses logprobs field

dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/AgentResponseExtensions.cs

@@ -53,6 +53,7 @@ public static Response ToResponse(
             Error = null,
             Id = context.ResponseId,
             Instructions = request.Instructions,
+            Logprobs = request.Logprobs,
             MaxOutputTokens = request.MaxOutputTokens,
             MaxToolCalls = request.MaxToolCalls,
             Metadata = request.Metadata is IReadOnlyDictionary<string, string> metadata ? new Dictionary<string, string>(metadata) : [],

dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/AgentResponseUpdateExtensions.cs

@@ -250,6 +250,7 @@ Response CreateResponse(ResponseStatus status = ResponseStatus.Completed, IEnume
                 Error = null,
                 Id = context.ResponseId,
                 Instructions = request.Instructions,
+                Logprobs = request.Logprobs,
                 MaxOutputTokens = request.MaxOutputTokens,
                 MaxToolCalls = request.MaxToolCalls,
                 Metadata = request.Metadata != null ? new Dictionary<string, string>(request.Metadata) : [],

dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/InMemoryResponsesService.cs

@@ -383,6 +383,7 @@ private ResponseState InitializeResponse(string responseId, CreateResponse reque
             Id = responseId,
             IncompleteDetails = null,
             Instructions = request.Instructions,
+            Logprobs = request.Logprobs,
             MaxOutputTokens = request.MaxOutputTokens,
             MaxToolCalls = request.MaxToolCalls,
             Metadata = metadata,

dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/Models/CreateResponse.cs

@@ -127,6 +127,12 @@ internal sealed class CreateResponse
     [JsonPropertyName("max_tool_calls")]
     public int? MaxToolCalls { get; init; }
 
+    /// <summary>
+    /// Whether to return log probabilities of the output tokens.
+    /// </summary>
+    [JsonPropertyName("logprobs")]
+    public bool? Logprobs { get; init; }
+
     /// <summary>
     /// An integer between 0 and 20 specifying the number of most likely tokens to return at each token position.
     /// </summary>

dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/Responses/Models/Response.cs

@@ -228,6 +228,12 @@ internal sealed record Response
     [JsonPropertyName("max_tool_calls")]
     public int? MaxToolCalls { get; init; }
 
+    /// <summary>
+    /// Whether log probabilities were requested for the output tokens.
+    /// </summary>
+    [JsonPropertyName("logprobs")]
+    public bool? Logprobs { get; init; }
+
     /// <summary>
     /// An integer between 0 and 20 specifying the number of most likely tokens to return at each token position.
     /// </summary>

dotnet/tests/Microsoft.Agents.AI.Hosting.OpenAI.UnitTests/OpenAIResponsesSerializationTests.cs

@@ -192,6 +192,31 @@ public void Serialize_CreateRequestWithOptions_IncludesAllFields()
         Assert.Equal("value2", metadata.GetProperty("key2").GetString());
     }
 
+    [Fact]
+    public void Deserialize_CreateResponseWithLogprobs_RoundTripsFields()
+    {
+        const string Json = """
+        {
+          "model": "gpt-4o-mini",
+          "input": "Return token probabilities.",
+          "logprobs": true,
+          "top_logprobs": 3
+        }
+        """;
+
+        CreateResponse? createResponse = JsonSerializer.Deserialize(Json, OpenAIHostingJsonContext.Default.CreateResponse);
+        string reserializedJson = JsonSerializer.Serialize(createResponse, OpenAIHostingJsonContext.Default.CreateResponse);
+        using var doc = JsonDocument.Parse(reserializedJson);
+        var root = doc.RootElement;
+
+        Assert.NotNull(createResponse);
+        Assert.True(createResponse.Logprobs.HasValue);
+        Assert.True(createResponse.Logprobs.Value);
+        Assert.Equal(3, createResponse.TopLogprobs);
+        Assert.True(root.GetProperty("logprobs").GetBoolean());
+        Assert.Equal(3, root.GetProperty("top_logprobs").GetInt32());
+    }
+
     [Fact]
     public void Serialize_NullableFields_AreOmittedWhenNull()
     {
@@ -535,6 +560,43 @@ public void Deserialize_MetadataResponse_HasModelParameters()
         Assert.Equal(150, response.MaxOutputTokens);
     }
 
+    [Fact]
+    public void Deserialize_ResponseWithLogprobs_RoundTripsFields()
+    {
+        const string Json = """
+        {
+          "id": "resp_logprobs",
+          "object": "response",
+          "created_at": 1715000000,
+          "model": "gpt-4o-mini",
+          "status": "completed",
+          "output": [],
+          "usage": {
+            "input_tokens": 0,
+            "input_tokens_details": { "cached_tokens": 0 },
+            "output_tokens": 0,
+            "output_tokens_details": { "reasoning_tokens": 0 },
+            "total_tokens": 0
+          },
+          "tools": [],
+          "logprobs": true,
+          "top_logprobs": 3
+        }
+        """;
+
+        Response? response = JsonSerializer.Deserialize(Json, OpenAIHostingJsonContext.Default.Response);
+        string reserializedJson = JsonSerializer.Serialize(response, OpenAIHostingJsonContext.Default.Response);
+        using var doc = JsonDocument.Parse(reserializedJson);
+        var root = doc.RootElement;
+
+        Assert.NotNull(response);
+        Assert.True(response.Logprobs.HasValue);
+        Assert.True(response.Logprobs.Value);
+        Assert.Equal(3, response.TopLogprobs);
+        Assert.True(root.GetProperty("logprobs").GetBoolean());
+        Assert.Equal(3, root.GetProperty("top_logprobs").GetInt32());
+    }
+
     [Fact]
     public void Deserialize_ToolCallResponse_HasFunctionCall()
     {