xAI releases Grok Voice Think Fast 2.0 speech-to-speech model for voice agents
Confirmed
The takeaway
On 2026-07-29 xAI (SpaceXAI) released Grok Voice Think Fast 2.0, a reasoning speech-to-speech model for its OpenAI-Realtime-compatible Voice Agent API at $0.08/min, scoring 82.9 on the Artificial Analysis Speech-to-Speech Quality Index and cutting time to first audio to 0.70 s.
Status
- Claim
Confirmed
- Our reporting
- High confidence
- Importance
- 3 of 5
- Last verified
- 29 September 2026
Your AI and this story
- GPT-6 Astra90 days after its cutoff
- Claude Opus 5.529 days after its cutoff
- Gemini 4 Hydrogen120 days after its cutoff
- Grok 4.759 days after its cutoff
None of these four assistants can know about it. The closest, Claude Opus 5.5, stops 29 days before it.
Key facts
- Model id grok-voice-think-fast-2.0; grok-voice-latest switched to it on 2026-08-05
- Price: $0.08 per minute of audio ($4.80/hr)
- AA Speech-to-Speech Quality Index 82.9% (v1.0: 75.7%); Big Bench Audio 97.2%; Full Duplex Bench 95.1%; tau-voice Bench 56.5% (xAI)
- Time to first audio 0.70 s (from 1.25 s)
- Transcription 1.5-2x better than Deepgram Nova 3 and ElevenLabs Scribe v2 across 24 languages, ~10x in noise (xAI)
- Starlink A/B test: higher sales conversion and support containment (xAI)
- Grok voice stack also includes Grok STT/TTS APIs (2026-04-17) and Grok Voice Transcribe 2.0 (2026-09-18, $0.10/hr)
What happened
xAI shipped the second generation of its realtime voice model, which reasons while it talks and can call web search, X search, file search and remote MCP tools from inside a voice session. It powers Grok’s voice mode, the Grok assistant in Tesla cars and Starlink support calls, and is exposed via a WebSocket API that mirrors OpenAI’s Realtime protocol.
Why it matters
Its reported AA S2S Quality Index (82.9) put it roughly level with Google’s Gemini 3.8 Live Extended Thinking (82.6, Sept 2026) and marked xAI’s push to compete on voice agents on price. Benchmarks are xAI-reported.
Sources
4 sources from 2 sites. Numbers match the chips in the text.
4 sources: 4 primary
Primary
- SpaceXAI - Grok Voice Think Fast 2.0x.ai, official
- xAI docs - Speech to Speech (Voice Agent API)docs.x.ai, docs
- SpaceXAI - Grok Voice Transcribe 2.0x.ai, official
- SpaceXAI - Grok Speech to Text and Text to Speech APIsx.ai, official
Changes
- Linked the Voice Agent Builder entry (2026-07-01)
- Filed