langchain-ai/deepagents · error · TypeError

LangGraph returned non-object thread state.

Error message

LangGraph returned non-object thread state.

What it means

After fetching thread state, the SDK expects LangGraph's `get_state` values to be an object (dict). If the server returns any other shape — null, a list, or a scalar — _hydrate_state raises this TypeError rather than crashing later with an opaque attribute error. This usually signals a server/runtime mismatch or corrupted thread state rather than a problem with your request.

Source

Thrown at libs/code/deepagents_code/offload_api.py:552

        {str(key): value for key, value in responses.items()},
    )


def _hydrate_state(values: object) -> _OffloadState:
    """Hydrate serialized checkpoint messages for the compaction service.

    Args:
        values: State values returned by LangGraph Server.

    Returns:
        A shallow state copy containing LangChain message objects.

    Raises:
        TypeError: If the server returns an unexpected state shape.
    """
    if not isinstance(values, dict):
        msg = "LangGraph returned non-object thread state."
        raise TypeError(msg)
    state = dict(values)
    messages = state.get("messages", [])
    if not isinstance(messages, list):
        msg = "LangGraph returned a non-list messages channel."
        raise TypeError(msg)
    state["messages"] = convert_to_messages(messages)

    # LangGraph serializes the summary stored inside the private event channel
    # independently of the top-level `messages` channel. The summarization SDK
    # prepends it to the effective conversation, so it must be a message object
    # too rather than the serialized dict returned by the thread API.
    event = state.get("_summarization_event")
    if isinstance(event, Mapping) and "summary_message" in event:
        hydrated_event = dict(event)
        summary_message = hydrated_event["summary_message"]
        hydrated_event["summary_message"] = convert_to_messages([summary_message])[0]
        state["_summarization_event"] = hydrated_event
    return cast("_OffloadState", state)

View on GitHub (pinned to a1af029e6e)

Solutions

1. Verify the thread server version matches the SDK's expected LangGraph threads API; upgrade the server or pin the SDK accordingly.
2. Confirm the thread_id exists (client.threads.get(thread_id)) before offloading; recreate the thread if its state is missing.
3. Catch TypeError around the offload call and surface 'unreadable thread state' to the user instead of retrying blindly.
4. Inspect the raw get_state response (log it) to see what shape is actually returned; check for proxies rewriting the body.

Example fix

// before
state = await offload(thread_id, payload)
// after
try:
    state = await offload(thread_id, payload)
except TypeError as exc:
    if "non-object thread state" in str(exc):
        raise RuntimeError(f"Thread {thread_id} state is unreadable; recreate the thread") from exc
    raise

before = await client.threads.get_state(thread_id)
if not isinstance(before, dict):
    raise RuntimeError(f"Thread {thread_id} returned non-object state; server/schema mismatch")

def is_thread_state(values) -> bool:
    return isinstance(values, dict)

try:
    state = await offload(thread_id, payload)
except TypeError as exc:
    if "non-object thread state" in str(exc):
        raise RuntimeError(
            f"Thread {thread_id} state is unreadable; verify server version or recreate the thread"
        ) from exc
    raise

When it happens

Trigger: _execute_offload calling client.threads.get_state(thread_id) and receiving values that is not a dict (None from an empty/unknown thread, a list, or a differently shaped payload from an incompatible server version).

Common situations: Pointing the client at an older/incompatible LangGraph thread server whose state schema differs, a thread id that exists but has no object-shaped state, proxy/gateway mangling the response body, or a mocked client in tests returning a non-dict.

Related errors

• LangGraph returned a non-list messages channel.
• -32002
• SHELL_ALLOW_ALL should not be used with ShellAllowListMiddle
• interpreter_ptc must be False, 'safe', 'all', or a list of t
• --model-params must be a JSON object, got {type}

AI-assisted analysis of langchain-ai/deepagents@a1af029e6e (2026-08-29). Data as JSON: /api/errors/7e8a93e57396c3f3. Report an issue: GitHub.