langchain-ai/langgraph · error · RuntimeError

Async model callable provided but agent invoked synchronousl

Error message

Async model callable provided but agent invoked synchronously. Use agent.ainvoke() or agent.astream(), or provide a sync model callable.

What it means

Error "Async model callable provided but agent invoked synchronously. Use agent.ainvoke() or agent.astream(), or provide a sync model callable." thrown in langchain-ai/langgraph.

Source

Thrown at libs/prebuilt/langgraph/prebuilt/chat_agent_executor.py:670

        # we're passing messages under `messages` key, as this is expected by the prompt
        if isinstance(state_schema, type) and issubclass(state_schema, BaseModel):
            state.messages = messages  # type: ignore
        else:
            state["messages"] = messages  # type: ignore

        return state

    # Define the function that calls the model
    def call_model(
        state: StateSchema, runtime: Runtime[ContextT], config: RunnableConfig
    ) -> StateSchema:
        if is_async_dynamic_model:
            msg = (
                "Async model callable provided but agent invoked synchronously. "
                "Use agent.ainvoke() or agent.astream(), or "
                "provide a sync model callable."
            )
            raise RuntimeError(msg)

        model_input = _get_model_input_state(state)

        if is_dynamic_model:
            # Resolve dynamic model at runtime and apply prompt
            dynamic_model = _resolve_model(state, runtime)
            response = cast(AIMessage, dynamic_model.invoke(model_input, config))  # type: ignore[arg-type]
        else:
            response = cast(AIMessage, static_model.invoke(model_input, config))  # type: ignore[union-attr]

        # add agent name to the AIMessage
        response.name = name

        if _are_more_steps_needed(state, response):
            return {
                "messages": [
                    AIMessage(
                        id=response.id,

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/prebuilt/langgraph/prebuilt/chat_agent_executor.py:670 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/6d40bab28e0bb079. Report an issue: GitHub.