langchain-ai/langgraph · error · TypeError

Object of type {type(obj)} is not JSON serializable

Error message

Object of type {type(obj)} is not JSON serializable

What it means

Error "Object of type {type(obj)} is not JSON serializable" thrown in langchain-ai/langgraph.

Source

Thrown at libs/sdk-py/langgraph_sdk/_shared/utilities.py:91

    is_class = isinstance(obj, type)
    if hasattr(obj, "model_dump") and callable(obj.model_dump):
        if is_class:
            raise TypeError(
                f"Cannot JSON-serialize type object: {obj!r}. Did you mean to pass an instance of the object instead?"
                f"\nReceived type: {obj!r}"
            )
        return obj.model_dump()
    elif hasattr(obj, "dict") and callable(obj.dict):
        if is_class:
            raise TypeError(
                f"Cannot JSON-serialize type object: {obj!r}. Did you mean to pass an instance of the object instead?"
                f"\nReceived type: {obj!r}"
            )
        return obj.dict()
    elif isinstance(obj, (set, frozenset)):
        return list(obj)
    else:
        raise TypeError(f"Object of type {type(obj)} is not JSON serializable")


# Compiled regex pattern for extracting run metadata from Content-Location header
_RUN_METADATA_PATTERN = re.compile(
    r"(\/threads\/(?P<thread_id>.+))?\/runs\/(?P<run_id>.+)"
)


def _get_run_metadata_from_response(
    response: httpx.Response,
) -> RunCreateMetadata | None:
    """Extract run metadata from the response headers."""
    if (content_location := response.headers.get("Content-Location")) and (
        match := _RUN_METADATA_PATTERN.search(content_location)
    ):
        return RunCreateMetadata(
            run_id=match.group("run_id"),
            thread_id=match.group("thread_id") or None,

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/sdk-py/langgraph_sdk/_shared/utilities.py:91 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/eaa1754882be755c. Report an issue: GitHub.