langchain-ai/langgraph · error · ValueError

Output channel '{chan}' not in known channels: '{repr(sorted

Error message

Output channel '{chan}' not in known channels: '{repr(sorted(channels))[:100]}'

What it means

Error "Output channel '{chan}' not in known channels: '{repr(sorted(channels))[:100]}'" thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/pregel/_validate.py:95

        if all(chan not in subscribed_channels for chan in input_channels):
            raise ValueError(
                f"None of the input channels {input_channels} "
                f"are subscribed to by any node"
            )

    all_output_channels = set[str]()
    if isinstance(output_channels, str):
        all_output_channels.add(output_channels)
    else:
        all_output_channels.update(output_channels)
    if isinstance(stream_channels, str):
        all_output_channels.add(stream_channels)
    elif stream_channels is not None:
        all_output_channels.update(stream_channels)

    for chan in all_output_channels:
        if chan not in channels:
            raise ValueError(
                f"Output channel '{chan}' not "
                f"in known channels: '{repr(sorted(channels))[:100]}'"
            )

    if interrupt_after_nodes != "*":
        for n in interrupt_after_nodes:
            if n not in nodes:
                raise ValueError(f"Node {n} not in nodes")
    if interrupt_before_nodes != "*":
        for n in interrupt_before_nodes:
            if n not in nodes:
                raise ValueError(f"Node {n} not in nodes")


def validate_keys(
    keys: str | Sequence[str] | None,
    channels: Mapping[str, Any],
) -> None:

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/pregel/_validate.py:95 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/405f375b3d069d93. Report an issue: GitHub.