Voice agent openers re-fire after barge-in: an xAI realtime engine timing bug
Kindly-Duty272 · reddit · 2026-09-27
A developer hit a recurring bug on xAI's realtime voice engine: with a fixed scripted opener, clean calls work fine, but if the caller barges in early (e.g., a quick "Hello?"), the agent re-speaks the same opener mid-sentence — the greeting gets queued twice after an interruption.
- Current workaround: drop the preset first message entirely and put the opener text in the system prompt so the callee speaks first — mostly avoids double-firing, but it's a workaround, not a fix.
- Suspected root cause: turn-detection timing. The server seems to have a 1.3s floor before deciding the caller finished, while their own VAD triggers faster (1.2s); the two clocks may race, causing opener replay.
- The author is surveying other stacks — Vapi, Retell, raw Twilio/Deepgram builds, LiveKit — to see if the issue is engine-specific turn handling or widespread.
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