langchain-ai/langgraph · error · RuntimeError

{type(self).__name__}.schedule() requires a running event lo

Error message

{type(self).__name__}.schedule() requires a running event loop; this transformer must run under astream(), not stream(). Set requires_async=True on the class so this fails at registration rather than at first event.

What it means

Error "{type(self).__name__}.schedule() requires a running event loop; this transformer must run under astream(), not stream(). Set requires_async=True on the class so this fails at registration rather than at first event." thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/stream/_types.py:271

            on_error: `"log"` (default) catches and logs any exception
                the coroutine raises, so a single failure doesn't tear
                down the run. `"raise"` lets the exception propagate
                when the mux joins pendings, converting the close path
                into the fail path.

        Returns:
            The asyncio Task. Authors rarely need to await it directly
            — consumers read results from whatever projection the
            coroutine pushes into.

        Raises:
            RuntimeError: If called without a running event loop (i.e.
                under sync `stream()` rather than `astream()`).
        """
        try:
            asyncio.get_running_loop()
        except RuntimeError:
            raise RuntimeError(
                f"{type(self).__name__}.schedule() requires a running "
                "event loop; this transformer must run under astream(), "
                "not stream(). Set requires_async=True on the class so "
                "this fails at registration rather than at first event."
            ) from None

        wrapped = self._wrap_scheduled(coro) if on_error == "log" else coro
        task = asyncio.create_task(wrapped)
        tasks = self._scheduled_task_set()
        tasks.add(task)
        task.add_done_callback(tasks.discard)
        return task

    @staticmethod
    async def _wrap_scheduled(coro: Coroutine[Any, Any, Any]) -> Any:
        try:
            return await coro
        except asyncio.CancelledError:

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/stream/_types.py:271 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/c96ea135e14e2cfa. Report an issue: GitHub.