OpenAI Multi-Agent Beta: Ship an Agent Tree in Python

OpenAI shipped a beta on the Responses API that changes what a single request can be. Set multi_agent.enabled to true and one request stops being one model turn. It becomes a tree: a root agent that can spawn subagents, hand them bounded tasks, message them, interrupt them, and wait on their replies, all inside the same response.

This matters right now because GPT-6 Astra landed on September 3 and the loudest take across dev communities has been that Astra is less a model release than an agent runtime. The delegation part of that runtime is not magic inside the weights. It is a documented API surface, and it is small enough to learn in an afternoon.