langchain-ai/langgraph · error · InvalidUpdateError

At key '{self.key}': UntrackedValue(guard=True) can receive

Error message

At key '{self.key}': UntrackedValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values.

What it means

Error "At key '{self.key}': UntrackedValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values." thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/channels/untracked_value.py:60

        """Return a copy of the channel."""
        empty = self.__class__(self.typ, self.guard)
        empty.key = self.key
        empty.value = self.value
        return empty

    def checkpoint(self) -> Value | Any:
        return MISSING

    def from_checkpoint(self, checkpoint: Value) -> Self:
        empty = self.__class__(self.typ, self.guard)
        empty.key = self.key
        return empty

    def update(self, values: Sequence[Value]) -> bool:
        if len(values) == 0:
            return False
        if len(values) != 1 and self.guard:
            raise InvalidUpdateError(
                f"At key '{self.key}': UntrackedValue(guard=True) can receive only one value per step. Use guard=False if you want to store any one of multiple values."
            )

        self.value = values[-1]
        return True

    def get(self) -> Value:
        if self.value is MISSING:
            raise EmptyChannelError()
        return self.value

    def is_available(self) -> bool:
        return self.value is not MISSING

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/channels/untracked_value.py:60 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/2f68dcd6e625245f. Report an issue: GitHub.