microsoft/autogen · error · ValueError

Unsupported payload serialization format: {payload_serializa

Error message

Unsupported payload serialization format: {payload_serialization_format}

What it means

GrpcWorkerAgentRuntime accepts a payload_serialization_format constructor argument that selects how message payloads cross the wire. Only the JSON and Protobuf content types (JSON_DATA_CONTENT_TYPE / PROTOBUF_DATA_CONTENT_TYPE) are implemented; anything else is rejected in __init__ with ValueError so misconfiguration fails before the runtime starts.

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/runtimes/grpc/_worker_runtime.py:257

        self._agent_factories: Dict[
            str, Callable[[], Agent | Awaitable[Agent]] | Callable[[AgentRuntime, AgentId], Agent | Awaitable[Agent]]
        ] = {}
        self._instantiated_agents: Dict[AgentId, Agent] = {}
        self._known_namespaces: set[str] = set()
        self._read_task: None | Task[None] = None
        self._running = False
        self._pending_requests: Dict[str, Future[Any]] = {}
        self._pending_requests_lock = asyncio.Lock()
        self._next_request_id = 0
        self._host_connection: HostConnection | None = None
        self._background_tasks: Set[Task[Any]] = set()
        self._subscription_manager = SubscriptionManager()
        self._serialization_registry = SerializationRegistry()
        self._extra_grpc_config = extra_grpc_config or []
        self._agent_instance_types: Dict[str, Type[Agent]] = {}

        if payload_serialization_format not in {JSON_DATA_CONTENT_TYPE, PROTOBUF_DATA_CONTENT_TYPE}:
            raise ValueError(f"Unsupported payload serialization format: {payload_serialization_format}")

        self._payload_serialization_format = payload_serialization_format

    async def start(self) -> None:
        """Start the runtime in a background task."""
        if self._running:
            raise ValueError("Runtime is already running.")
        logger.info(f"Connecting to host: {self._host_address}")
        self._host_connection = await HostConnection.from_host_address(
            self._host_address, extra_grpc_config=self._extra_grpc_config
        )
        logger.info("Connection established")
        if self._read_task is None:
            self._read_task = asyncio.create_task(self._run_read_loop())
        self._running = True

    def _raise_on_exception(self, task: Task[Any]) -> None:
        exception = task.exception()

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Use one of the supported constants: autogen_core.application JSON_DATA_CONTENT_TYPE ('application/json') or PROTOBUF_DATA_CONTENT_TYPE ('application/x-protobuf')
2. For custom payload types, register a serializer with the runtime's serialization registry and keep the wire format as JSON or protobuf
3. If you truly need a new wire format, subclass/extend the runtime rather than passing an unknown string

Example fix

# before
runtime = GrpcWorkerAgentRuntime(host_address, payload_serialization_format="msgpack")

# after
from autogen_ext.runtimes.grpc._constants import PROTOBUF_DATA_CONTENT_TYPE
runtime = GrpcWorkerAgentRuntime(host_address, payload_serialization_format=PROTOBUF_DATA_CONTENT_TYPE)

from autogen_ext.runtimes.grpc._constants import JSON_DATA_CONTENT_TYPE, PROTOBUF_DATA_CONTENT_TYPE

SUPPORTED_FORMATS = {JSON_DATA_CONTENT_TYPE, PROTOBUF_DATA_CONTENT_TYPE}
assert payload_serialization_format in SUPPORTED_FORMATS, f"use one of {SUPPORTED_FORMATS}"

try:
    runtime = GrpcWorkerAgentRuntime(host, payload_serialization_format=fmt)
except ValueError as e:
    if "serialization format" in str(e):
        fmt = JSON_DATA_CONTENT_TYPE
        runtime = GrpcWorkerAgentRuntime(host, payload_serialization_format=fmt)
    else:
        raise

When it happens

Trigger: Constructing GrpcWorkerAgentRuntime(host_address=..., payload_serialization_format='application/x-my-format') or any string other than the two supported content-type constants.

Common situations: Assuming an arbitrary MIME type or serializer name works; passing a custom serialization registry format id instead of the content-type constant; copy-paste from docs showing protobuf while sending a custom string.

Related errors

• Unsupported message content type: {message_content_type}
• Unsupported subscription type.
• Invalid subscription message.
• Root types cannot be derived from each other: {rootType.Name
• Tool names must be unique: {tool_names}

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/4cd66ab3ac75a99c. Report an issue: GitHub.