Three acknowledgements you cannot wait for

A Voice Comic demo built on Deepgram’s Voice Agent API illustrates how mid-call changes to speech recognition models, language models, and voices can succeed server-side even when expected WebSocket acknowledgements such as ListenUpdated or ThinkUpdated fail to reach the client. To prevent the interface from remaining stuck during model changes, the implementation treats acknowledgements as a fast path and uses a three-second timeout that silently reconnects with fresh Settings, no greeting, and a resume identifier to preserve session-related state. The author found that UpdateListen acknowledgements were intermittently missing, especially when switching between Flux STT v2 and Nova-3 v1, while UpdateThink acknowledgements could disappear when sent immediately alongside UpdateListen, leading to a recommendation to sequence LLM changes separately or include both settings in a reconnect. The demo also distinguishes idle-stream behavior by keeping the agent and Nova-3 streams alive with periodic KeepAlive messages while closing and reopening Flux STT streams, whose v2 endpoint does not support KeepAlive; because Flux turn indexes restart on each new socket, the UI combines a socket epoch with the turn index to avoid overwriting prior transcript panels. SpeakUpdated acknowledgements were consistently received in the author’s tests, so voice changes do not use the fallback timer, and the project includes a public repository, hosted demo, event log, and live tests for reproducing the behavior.

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