{"record":{"id":"9f7e6baebe0cab82","repo":"langchain-ai/langgraph","slug":"stream-events-version-v3-transformers-must-be-s","errorCode":null,"errorMessage":"stream_events(version='v3') transformers must be scope-aware callables, got pre-built instance {type(spec).__name__}. Pass the transformer class or a factory like `lambda scope: MyTransformer(scope, ...)`.","messagePattern":"stream_events\\(version='v3'\\) transformers must be scope-aware callables, got pre-built instance (.+?)\\. Pass the transformer class or a factory like `lambda scope: MyTransformer\\(scope, \\.\\.\\.\\)`\\.","errorType":"exception","errorClass":"TypeError","httpStatus":null,"severity":"error","filePath":"libs/langgraph/langgraph/pregel/main.py","lineNumber":431,"sourceCode":"        )\n    return list(modes)\n\n\ndef _normalize_stream_transformer_factories(\n    specs: Sequence[Callable[[tuple[str, ...]], Any]] | None,\n) -> list[Callable[[tuple[str, ...]], Any]]:\n    \"\"\"Normalize stream transformer specs to scoped factories.\n\n    A stream transformer spec is a callable that accepts\n    `scope: tuple[str, ...]` and returns a fresh `StreamTransformer`.\n    Transformer classes work when their constructor follows the same\n    shape. Pre-built instances are rejected because they cannot be\n    cloned into subgraph scopes.\n    \"\"\"\n    factories: list[Callable[[tuple[str, ...]], Any]] = []\n    for spec in specs or ():\n        if isinstance(spec, StreamTransformer):\n            raise TypeError(\n                \"stream_events(version='v3') transformers must be scope-aware callables, \"\n                f\"got pre-built instance {type(spec).__name__}. Pass the \"\n                \"transformer class or a factory like \"\n                \"`lambda scope: MyTransformer(scope, ...)`.\"\n            )\n        if not callable(spec):\n            raise TypeError(\n                \"stream_events(version='v3') transformers must be scope-aware callables, \"\n                f\"got {type(spec).__name__}.\"\n            )\n\n        def factory(scope: tuple[str, ...], _spec: Callable[..., Any] = spec) -> Any:\n            return _spec(scope)\n\n        factories.append(factory)\n    return factories\n\n","sourceCodeStart":413,"sourceCodeEnd":449,"githubUrl":"https://github.com/langchain-ai/langgraph/blob/38031739e551638e373fb553453256c23feeb41f/libs/langgraph/langgraph/pregel/main.py#L413-L449","documentation":"Error \"stream_events(version='v3') transformers must be scope-aware callables, got pre-built instance {type(spec).__name__}. Pass the transformer class or a factory like `lambda scope: MyTransformer(scope, ...)`.\" thrown in langchain-ai/langgraph.","triggerScenarios":"Thrown at libs/langgraph/langgraph/pregel/main.py:431 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"}