{"record":{"id":"c4fb38658a58dce4","repo":"langchain-ai/langgraph","slug":"invalid-concurrent-graph-update-c4fb38","errorCode":"INVALID_CONCURRENT_GRAPH_UPDATE","errorMessage":"At key '{self.key}': Can receive only one value per step. Use an Annotated key to handle multiple values.","messagePattern":"At key '(.+?)': Can receive only one value per step\\. Use an Annotated key to handle multiple values\\.","errorType":"validation","errorClass":"InvalidUpdateError","httpStatus":null,"severity":"error","filePath":"libs/langgraph/langgraph/channels/last_value.py","lineNumber":64,"sourceCode":"        empty = self.__class__(self.typ, self.key)\n        empty.value = self.value\n        return empty\n\n    def from_checkpoint(self, checkpoint: Value) -> Self:\n        empty = self.__class__(self.typ, self.key)\n        if checkpoint is not MISSING:\n            empty.value = checkpoint\n        return empty\n\n    def update(self, values: Sequence[Value]) -> bool:\n        if len(values) == 0:\n            return False\n        if len(values) != 1:\n            msg = create_error_message(\n                message=f\"At key '{self.key}': Can receive only one value per step. Use an Annotated key to handle multiple values.\",\n                error_code=ErrorCode.INVALID_CONCURRENT_GRAPH_UPDATE,\n            )\n            raise InvalidUpdateError(msg)\n\n        self.value = values[-1]\n        return True\n\n    def get(self) -> Value:\n        if self.value is MISSING:\n            raise EmptyChannelError()\n        return self.value\n\n    def is_available(self) -> bool:\n        return self.value is not MISSING\n\n    def checkpoint(self) -> Value:\n        return self.value\n\n\nclass LastValueAfterFinish(\n    Generic[Value], BaseChannel[Value, Value, tuple[Value, bool]]","sourceCodeStart":46,"sourceCodeEnd":82,"githubUrl":"https://github.com/langchain-ai/langgraph/blob/38031739e551638e373fb553453256c23feeb41f/libs/langgraph/langgraph/channels/last_value.py#L46-L82","documentation":"Error \"At key '{self.key}': Can receive only one value per step. Use an Annotated key to handle multiple values.\" thrown in langchain-ai/langgraph.","triggerScenarios":"Thrown at libs/langgraph/langgraph/channels/last_value.py:64 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"38031739e551638e373fb553453256c23feeb41f","analyzedAt":"2026-08-26T18:02:49.312Z","schemaVersion":2},"datasetVersion":"2026-08-26T21:11:00.512Z"}