Agent ABC — and the manifest
loads it the same way it loads a tool module.
The Agent contract
The whole agent shape is owned once by the contract: theAgent ABC with its
default stream and drain behaviour, the neutral spec descriptors, and a typed
event vocabulary. The skeleton adds no agent implementation of its own — it
surfaces the contract in its own namespace and registers agents against the app.
You register an agent with a decorator that also names it. The skeleton
synthesizes the agent’s JSON run tool from its declared input model, so an agent
is callable exactly like any other tool:
Streaming events
An agent run streams a typed sequence ofStreamEvents rather than returning a
single blob. The vocabulary covers message deltas and finals, reasoning steps,
tool-call and tool-result steps, structured finals, interrupt finals, and run
usage. The event producers — the projection over the agent runtime’s updates and
messages — live in the agents runtime; a client renders the frames as they arrive.
Run an agent and watch its stream from the CLI:
Authored agents
Beyond code-defined agents, you can author an agent as a saved spec that rides the versioning spine — a preset that bakes the agent’s preset-bakeable fields. Authored agents version and roll back exactly like presets, so an agent’s configuration evolves without breaking its callers.Composition
An agent can drive other agents as sub-agents and chain multi-step work. That compositional side — sub-agents and the ready-made set — is its own pillar: deep agents. See the author-an-agent guide for the full authoring path and the Python SDK reference for theAgent
ABC and the StreamEvent types.