langchain-ai/langgraph · error · RuntimeError

Protocol command did not return a valid response.

Error message

Protocol command did not return a valid response.

What it means

Error "Protocol command did not return a valid response." thrown in langchain-ai/langgraph.

Source

Thrown at libs/sdk-py/langgraph_sdk/stream/transport/http.py:85

        Raises:
            httpx.HTTPStatusError: server returned >= 400.
            RuntimeError: the transport has been closed via `close()`.
            RuntimeError: server returned a response missing the protocol envelope.
        """
        if self._closed:
            raise RuntimeError("Protocol transport is closed.")
        # Merge default headers first so content-type always wins.
        merged_headers = {**self._default_headers, "content-type": "application/json"}
        response = await self._client.post(
            self._commands_url,
            content=orjson.dumps(command),
            headers=merged_headers,
        )
        response.raise_for_status()
        if response.status_code in (202, 204):
            return None
        if not response.content:
            raise RuntimeError("Protocol command did not return a valid response.")
        try:
            payload = orjson.loads(response.content)
        except orjson.JSONDecodeError as err:
            raise RuntimeError(
                "Protocol command did not return a valid response."
            ) from err
        if not isinstance(payload, dict) or "id" not in payload:
            raise RuntimeError("Protocol command did not return a valid response.")
        return payload

    def open_event_stream(self, params: dict[str, Any]) -> EventStreamHandle:
        """Open an independent filtered SSE event stream.

        Posts `params` as a SubscribeParams body to `/threads/{thread_id}/stream/events`.
        Returns an `EventStreamHandle` whose `events` async iterator yields typed
        `Event` dicts as the server emits them. `handle.ready` resolves on a 2xx
        response (rejects on HTTP error or transport failure before headers).

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/sdk-py/langgraph_sdk/stream/transport/http.py:85 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/cb185f6d2771921d. Report an issue: GitHub.