OptionalresponseOpenAI populates usage here. xAI sends this present but EMPTY.
Typed as unknown deliberately: this is untrusted wire data, and each provider SDK declares
its own concrete usage interface (without the index signature RealtimeResponseDoneUsage
carries). Accepting unknown lets every SDK's frame type be passed in directly — no cast at
the call site — while ResolveResponseDoneUsage does the narrowing centrally.
OptionalusagexAI populates usage here, as a sibling of response. OpenAI omits it.
A
response.doneframe, declaring BOTH slots the OpenAI-compatible providers use for usage. See ResolveResponseDoneUsage.