microsoft/autogen · error · InvalidOperationException

Unsupported message type: {reply.GetType()}

Error message

Unsupported message type: {reply.GetType()}

What it means

Thrown by GeminiMessageConnector's STREAMING path when strictMode is enabled and the agent's streaming reply item is not IMessage<GenerateContentResponse>. In strict mode the connector refuses to pass through foreign message types; non-strict mode simply yields them unchanged.

Source

Thrown at dotnet/src/AutoGen.Gemini/Middleware/GeminiMessageConnector.cs:69

            {
                // if m.Content is empty and stop reason is Stop, ignore the message
                if (m.Content.Candidates.Count == 1 && m.Content.Candidates[0].Content.Parts.Count == 1 && m.Content.Candidates[0].Content.Parts[0].DataCase == Part.DataOneofCase.Text)
                {
                    var text = m.Content.Candidates[0].Content.Parts[0].Text;
                    var stopReason = m.Content.Candidates[0].FinishReason;
                    if (string.IsNullOrEmpty(text) && stopReason == FinishReason.Stop)
                    {
                        continue;
                    }
                }

                bucket.Add(m.Content);

                yield return PostProcessStreamingMessage(m.Content, agent);
            }
            else if (strictMode)
            {
                throw new InvalidOperationException($"Unsupported message type: {reply.GetType()}");
            }
            else
            {
                yield return reply;
            }

            // aggregate the message updates from bucket into a single message
            if (bucket is { Count: > 0 })
            {
                var isTextMessageUpdates = bucket.All(m => m.Candidates.Count == 1 && m.Candidates[0].Content.Parts.Count == 1 && m.Candidates[0].Content.Parts[0].DataCase == Part.DataOneofCase.Text);
                var isFunctionCallUpdates = bucket.Any(m => m.Candidates.Count == 1 && m.Candidates[0].Content.Parts.Count == 1 && m.Candidates[0].Content.Parts[0].DataCase == Part.DataOneofCase.FunctionCall);
                if (isTextMessageUpdates)
                {
                    var text = string.Join(string.Empty, bucket.Select(m => m.Candidates[0].Content.Parts[0].Text));
                    var textMessage = new TextMessage(Role.Assistant, text, agent.Name);

                    yield return textMessage;
                }

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Register GeminiMessageConnector directly against the GeminiChatAgent so it sees raw GenerateContentResponse streams (use the provided agent-registration helper for correct ordering)
2. Run the connector in non-strict mode (default) so foreign types pass through untouched
3. Remove any middleware between the Gemini agent and the connector that pre-converts messages

Example fix

// before:
var agent = new GeminiChatAgent(...).RegisterStreamingMiddleware(new GeminiMessageConnector(strictMode: true));
// middleware ordering yields Core types into connector -> throw
// after:
var agent = new GeminiChatAgent(...).RegisterMessageConnector(); // correct order, default non-strict

null

static bool IsGeminiStreamingReply(IMessage m) => m is IMessage<GenerateContentResponse>;

try { await foreach (var m in streamingGeminiAgent.GenerateStreamingReplyAsync(msgs, ct)) { } }
catch (InvalidOperationException e) when (e.Message.Contains("Unsupported message type") && strictMode)
{ /* rerun with non-strict connector: new GeminiMessageConnector() */ }

When it happens

Trigger: Constructing GeminiMessageConnector(strictMode: true) and having the wrapped streaming agent yield AutoGen Core message types (TextMessageUpdate, ToolCallMessageUpdate, MessageEnvelope of other payloads) instead of Gemini GenerateContentResponse envelopes.

Common situations: Composing middleware where another middleware already converted chunks to Core types before the connector sees them, or wrapping a non-Gemini streaming agent by mistake.

Related errors

• The first message is ToolCallMessage, but the update message
• The message is not a valid message
• The recent update is not a TextMessage
• The recent update is not a ToolCallMessage
• Message type {m.GetType()} is not supported.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/7e1f84ddd743f976. Report an issue: GitHub.