microsoft/autogen · error · CantHandleException

If agent_type is not specified DefaultSubscription must be c

Error message

If agent_type is not specified DefaultSubscription must be created within the subscription callback in AgentRuntime.register

What it means

Error "If agent_type is not specified DefaultSubscription must be created within the subscription callback in AgentRuntime.register" thrown in microsoft/autogen.

Source

Thrown at python/packages/autogen-core/src/autogen_core/_default_subscription.py:25

from .exceptions import CantHandleException


class DefaultSubscription(TypeSubscription):
    """The default subscription is designed to be a sensible default for applications that only need global scope for agents.

    This topic by default uses the "default" topic type and attempts to detect the agent type to use based on the instantiation context.

    Args:
        topic_type (str, optional): The topic type to subscribe to. Defaults to "default".
        agent_type (str, optional): The agent type to use for the subscription. Defaults to None, in which case it will attempt to detect the agent type based on the instantiation context.
    """

    def __init__(self, topic_type: str = "default", agent_type: str | AgentType | None = None):
        if agent_type is None:
            try:
                agent_type = SubscriptionInstantiationContext.agent_type().type
            except RuntimeError as e:
                raise CantHandleException(
                    "If agent_type is not specified DefaultSubscription must be created within the subscription callback in AgentRuntime.register"
                ) from e

        super().__init__(topic_type, agent_type)


BaseAgentType = TypeVar("BaseAgentType", bound="BaseAgent")


@overload
def default_subscription() -> Callable[[Type[BaseAgentType]], Type[BaseAgentType]]: ...


@overload
def default_subscription(cls: Type[BaseAgentType]) -> Type[BaseAgentType]: ...


def default_subscription(

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Create it inside AgentRuntime.register's callback or pass agent_type explicitly

Example fix

DefaultSubscription(agent_type="my_agent") or use within register(callback)

When it happens

Trigger: Thrown at python/packages/autogen-core/src/autogen_core/_default_subscription.py:25 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/e2ad1ebd793ef5a1. Report an issue: GitHub.