langchain-ai/langgraph · error · ValueError

Attempting to delete a message with an ID that doesn't exist

Error message

Attempting to delete a message with an ID that doesn't exist ('{m.id}')

What it means

Error "Attempting to delete a message with an ID that doesn't exist ('{m.id}')" thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/graph/message.py:228

            remove_all_idx = idx

    if remove_all_idx is not None:
        return right[remove_all_idx + 1 :]

    # merge
    merged = left.copy()
    merged_by_id = {m.id: i for i, m in enumerate(merged)}
    ids_to_remove = set()
    for m in right:
        if (existing_idx := merged_by_id.get(m.id)) is not None:
            if isinstance(m, RemoveMessage):
                ids_to_remove.add(m.id)
            else:
                ids_to_remove.discard(m.id)
                merged[existing_idx] = m
        else:
            if isinstance(m, RemoveMessage):
                raise ValueError(
                    f"Attempting to delete a message with an ID that doesn't exist ('{m.id}')"
                )

            merged_by_id[m.id] = len(merged)
            merged.append(m)
    merged = [m for m in merged if m.id not in ids_to_remove]

    if format == "langchain-openai":
        merged = _format_messages(merged)
    elif format:
        msg = f"Unrecognized {format=}. Expected one of 'langchain-openai', None."
        raise ValueError(msg)
    else:
        pass

    return merged

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/graph/message.py:228 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/4de2f8c1251bef37. Report an issue: GitHub.