microsoft/autogen · error · InvalidOperationException

The agent did not produce a final response. Check the agent'

Error message

The agent did not produce a final response. Check the agent's on_messages_stream method.

What it means

ChatAgentRouter drains an agent's chat stream (StreamAsync) and requires at least one ChatStreamFrame of FrameType.Response; each Response frame sets the local 'response' variable. If the stream ends with only Text/Output/InternalMessage frames (response stays null), HandleAsync throws InvalidOperationException after forwarding the partial messages, so the parent never receives a GroupChatAgentResponse.

Source

Thrown at dotnet/src/Microsoft.AutoGen/AgentChat/GroupChat/ChatAgentRouter.cs:86

        // the lack of real type unions in C#, which is why we need to create the StreamingFrame type in the first
        // place.
        await foreach (ChatStreamFrame frame in this.agent.StreamAsync(this.MessageBuffer, messageContext.CancellationToken))
        {
            switch (frame.Type)
            {
                case ChatStreamFrame.FrameType.Response:
                    await this.PublishMessageAsync(new GroupChatMessage { Message = frame.Response!.Message }, this.outputTopic);
                    response = frame.Response;
                    break;
                case ChatStreamFrame.FrameType.InternalMessage:
                    await this.PublishMessageAsync(new GroupChatMessage { Message = frame.InternalMessage! }, this.outputTopic);
                    break;
            }
        }

        if (response == null)
        {
            throw new InvalidOperationException("The agent did not produce a final response. Check the agent's on_messages_stream method.");
        }

        this.MessageBuffer.Clear();

        await this.PublishMessageAsync(new GroupChatAgentResponse { AgentResponse = response }, this.parentTopic);
    }

    public ValueTask HandleAsync(GroupChatReset item, MessageContext messageContext)
    {
        this.MessageBuffer.Clear();
        return this.agent.ResetAsync(messageContext.CancellationToken);
    }

    async ValueTask<JsonElement> ISaveState.SaveStateAsync()
    {
        ChatAgentContainerState state = new ChatAgentContainerState
        {
            AgentState = new SerializedState(await this.agent.SaveStateAsync()),

View on GitHub (pinned to 027ecf0a37)

Solutions

Fix the agent so its HandleAsync stream always ends with a ChatStreamFrame(FrameType.Response, response) before completion
Check middleware around the agent for dropped frames, especially filters on frame type
If early termination is intentional, still synthesize and emit a final Response frame (e.g. from the last partial message) before ending the stream

Example fix

// before (IChatAgent.HandleAsync stream)
await foreach (var chunk in source) yield return ChunkFrame(chunk); // no Response frame
// after
await foreach (var chunk in source) yield return ChunkFrame(chunk);
yield return ResponseFrame(new ChatMessageResponse(finalMessage, innerMessages));

Defensive patterns

Strategy: try-catch

Try / catch

try { await team.RunAsync(task, ct); }
catch (InvalidOperationException ex) when (ex.Message.Contains("did not produce a final response"))
{
    // inspect the agent's HandleAsync stream: it ended without a Response frame; fix the agent or its middleware
}

Prevention

Every IChatAgent's HandleAsync stream must end with a Response frame, including on early termination
Test each agent standalone (stream it directly) before adding it to a team
Audit frame-filtering middleware so it never drops FrameType.Response

When it happens

Trigger: Running a group chat where the selected agent's streaming implementation completes without a Response frame — e.g. an agent that streams only text chunks and returns, max-turn/early-exit logic that skips the final frame, or a custom IChatAgent adapter that forgets to yield the response frame.

Common situations: Plugging third-party or hand-rolled IChatAgent implementations into a team; agents whose HandleAsync stream finishes on a termination keyword before emitting the final response; middleware that filters the response frame out of the stream.

Related errors

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/acab0f295953a1b7. Report an issue: GitHub.