langchain-ai/langgraph · error · TypeError

Expected a Pydantic model. Got {type(model)}

Error message

Expected a Pydantic model. Got {type(model)}

What it means

Error "Expected a Pydantic model. Got {type(model)}" thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/_internal/_pydantic.py:51

@overload
def get_fields(model: type[BaseModel]) -> dict[str, FieldInfo]: ...


@overload
def get_fields(model: BaseModel) -> dict[str, FieldInfo]: ...


def get_fields(
    model: type[BaseModel] | BaseModel,
) -> dict[str, FieldInfo]:
    """Get the field names of a Pydantic model."""
    if hasattr(model, "model_fields"):
        return model.model_fields

    if hasattr(model, "__fields__"):
        return model.__fields__
    msg = f"Expected a Pydantic model. Got {type(model)}"
    raise TypeError(msg)


_SchemaConfig = ConfigDict(
    arbitrary_types_allowed=True, frozen=True, protected_namespaces=()
)

NO_DEFAULT = object()


def _create_root_model(
    name: str,
    type_: Any,
    module_name: str | None = None,
    default_: object = NO_DEFAULT,
) -> type[BaseModel]:
    """Create a base class."""

    def schema(

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/_internal/_pydantic.py:51 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/4cce76d2a578e432. Report an issue: GitHub.