{"record":{"id":"393db5240c4d3723","repo":"langchain-ai/langgraph","slug":"cannot-set-reserved-header-header","errorCode":null,"errorMessage":"Cannot set reserved header '{header}'","messagePattern":"Cannot set reserved header '(.+?)'","errorType":"exception","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"libs/sdk-py/langgraph_sdk/_shared/utilities.py","lineNumber":59,"sourceCode":"        return api_key\n    if api_key is NOT_PROVIDED:\n        # api_key is not explicitly provided, try to load from environment\n        for prefix in [\"LANGGRAPH\", \"LANGSMITH\", \"LANGCHAIN\"]:\n            if env := os.getenv(f\"{prefix}_API_KEY\"):\n                return env.strip().strip('\"').strip(\"'\")\n    # api_key is explicitly None, don't load from environment\n    return None\n\n\ndef _get_headers(\n    api_key: str | None,\n    custom_headers: Mapping[str, str] | None,\n) -> dict[str, str]:\n    \"\"\"Combine api_key and custom user-provided headers.\"\"\"\n    custom_headers = custom_headers or {}\n    for header in RESERVED_HEADERS:\n        if header in custom_headers:\n            raise ValueError(f\"Cannot set reserved header '{header}'\")\n\n    headers = {\n        \"User-Agent\": f\"langgraph-sdk-py/{langgraph_sdk.__version__}\",\n        **custom_headers,\n    }\n    resolved_api_key = _get_api_key(api_key)\n    if resolved_api_key:\n        headers[\"x-api-key\"] = resolved_api_key\n\n    return headers\n\n\ndef _orjson_default(obj: Any) -> Any:\n    is_class = isinstance(obj, type)\n    if hasattr(obj, \"model_dump\") and callable(obj.model_dump):\n        if is_class:\n            raise TypeError(\n                f\"Cannot JSON-serialize type object: {obj!r}. Did you mean to pass an instance of the object instead?\"","sourceCodeStart":41,"sourceCodeEnd":77,"githubUrl":"https://github.com/langchain-ai/langgraph/blob/38031739e551638e373fb553453256c23feeb41f/libs/sdk-py/langgraph_sdk/_shared/utilities.py#L41-L77","documentation":"Error \"Cannot set reserved header '{header}'\" thrown in langchain-ai/langgraph.","triggerScenarios":"Thrown at libs/sdk-py/langgraph_sdk/_shared/utilities.py:59 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"}