langchain-ai/langgraph · error · TypeError

Unsupported node type: {type(node)}

Error message

Unsupported node type: {type(node)}

What it means

Error "Unsupported node type: {type(node)}" thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/graph/state.py:128

def _warn_invalid_state_schema(schema: type[Any] | Any) -> None:
    if isinstance(schema, type):
        return
    if typing.get_args(schema):
        return
    warnings.warn(
        f"Invalid state_schema: {schema}. Expected a type or Annotated[type, reducer]. "
        "Please provide a valid schema to ensure correct updates.\n"
        " See: https://langchain-ai.github.io/langgraph/reference/graphs/#stategraph"
    )


def _get_node_name(node: StateNode[Any, ContextT]) -> str:
    try:
        return getattr(node, "__name__", node.__class__.__name__)
    except AttributeError:
        raise TypeError(f"Unsupported node type: {type(node)}")


class StateGraph(Generic[StateT, ContextT, InputT, OutputT]):
    """A graph whose nodes communicate by reading and writing to a shared state.

    The signature of each node is `State -> Partial<State>`.

    Each state key can optionally be annotated with a reducer function that
    will be used to aggregate the values of that key received from multiple nodes.
    The signature of a reducer function is `(Value, Value) -> Value`.

    !!! warning

        `StateGraph` is a builder class and cannot be used directly for execution.
        You must first call `.compile()` to create an executable graph that supports
        methods like `invoke()`, `stream()`, `astream()`, and `ainvoke()`. See the
        `CompiledStateGraph` documentation for more details.

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/graph/state.py:128 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/2a85fcbcf42ce5d9. Report an issue: GitHub.