microsoft/autogen · error · ValueError

No messages received from assistant

Error message

No messages received from assistant

What it means

After a run completes, OpenAIAssistantAgent lists the thread's messages (order=desc, limit=1) and expects at least one assistant message. An empty result — the thread has no messages at all — raises this. It typically means the message-create call before the run failed silently, the run completed without producing output, or the wrong thread was queried.

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/agents/openai/_openai_assistant_agent.py:505

                        )
                    )
                )
                continue

            if run.status == "completed":
                break

            await asyncio.sleep(0.5)

        # Get messages after run completion
        assistant_messages: AsyncCursorPage[Message] = await cancellation_token.link_future(
            asyncio.ensure_future(
                self._client.beta.threads.messages.list(thread_id=self._thread_id, order="desc", limit=1)  # type: ignore[reportDeprecated]
            )
        )

        if not assistant_messages.data:
            raise ValueError("No messages received from assistant")

        # Get the last message's content
        last_message = assistant_messages.data[0]
        if not last_message.content:
            raise ValueError(f"No content in the last message: {last_message}")

        # Extract text content
        text_content = [content for content in last_message.content if content.type == "text"]
        if not text_content:
            raise ValueError(f"Expected text content in the last message: {last_message.content}")

        # Return the assistant's response as a Response with inner messages
        chat_message = TextMessage(source=self.name, content=text_content[0].text.value)
        yield Response(chat_message=chat_message, inner_messages=inner_messages)

    async def handle_incoming_message(self, message: BaseChatMessage, cancellation_token: CancellationToken) -> None:
        """Handle regular text messages by adding them to the thread."""
        content: str | List[MessageContentPartParam] | None = None

View on GitHub (pinned to 027ecf0a37)

Solutions

  1. Retry the call — transient empty responses from the messages endpoint usually resolve on a second attempt.
  2. Verify the thread: list messages yourself with client.beta.threads.messages.list(thread_id=...) and confirm the thread contains the user message and run output.
  3. If the thread was deleted/reset, start a fresh conversation (new thread) instead of reusing the stale thread_id.

Example fix

# before
resp = await agent.on_messages([msg], ct)  # raises: No messages received

# after
for attempt in range(3):
    try:
        resp = await agent.on_messages([msg], ct)
        break
    except ValueError as e:
        if "No messages received" not in str(e) or attempt == 2:
            raise
        await asyncio.sleep(2)
Defensive patterns

Strategy: retry

Validate before calling

msgs_page = await agent.messages.list(thread_id=agent._thread_id, limit=5)
if not msgs_page.data:
    raise RuntimeError("thread is empty; start a new conversation")

Try / catch

for attempt in range(3):
    try:
        resp = await agent.on_messages(msgs, ct)
        break
    except ValueError as e:
        if "No messages received" not in str(e) or attempt == 2:
            raise
        await asyncio.sleep(2)

Prevention

When it happens

Trigger: Run lifecycle completes (status not failed/requires_action) but the thread contains no messages; thread_id pointing at an empty/newly created thread; messages created but later deleted; API replication lag returning an empty page.

Common situations: Reusing a thread_id from another workspace/deleted thread; on_reset deleting messages and a subsequent run misbehaving; transient API issues dropping the user message create.

Related errors

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/6f79d9e06b930dd1. Report an issue: GitHub.