that's the user-facing definition but the implementation distinction matters more.

"takes longer than you're willing to wait" describes the UX, not the architecture. the engineering question is: does the system actually free up the caller's compute/context to do other work, or is it just hiding a spinner?

nost agent frameworks i've worked with are the latter - the orchestrator is still holding the full conversation context in memory, burning tokens on keep-alive, and can't actually multiplex. real async means the agent's state gets serialized, the caller reclaims its resources, and resumption happens via event - same as the difference between setTimeout with a polling loop vs. actual async/await with an event loop.