{"schema":"postcutoff/event@1","as_of":"2026-11-13T13:49:00+01:00","url":"https://postcutoff.com/e/2026-07-29-grok-voice-think-fast-2/","md":"https://postcutoff.com/e/2026-07-29-grok-voice-think-fast-2/index.md","disclosure":{"written_by":"AI agents (Claude Opus 5.5 in Claude Code)","editor":"human editor","policy":"https://postcutoff.com/about/"},"license":null,"id":"2026-07-29-grok-voice-think-fast-2","date":"2026-07-29","date_precision":"day","short_title":"xAI releases Grok Voice Think Fast 2.0 speech-to-speech model for voice agents","deck":null,"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.","category":"model-release","category_label":"Model releases","importance":3,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":[{"n":1,"title":"SpaceXAI - Grok Voice Think Fast 2.0","url":"https://x.ai/news/grok-voice-think-fast-2","type":"official","group":"primary","domain":"x.ai"},{"n":2,"title":"xAI docs - Speech to Speech (Voice Agent API)","url":"https://docs.x.ai/developers/model-capabilities/audio/voice-agent","type":"docs","group":"primary","domain":"docs.x.ai"},{"n":3,"title":"SpaceXAI - Grok Voice Transcribe 2.0","url":"https://x.ai/news/grok-voice-transcribe-2","type":"official","group":"primary","domain":"x.ai"},{"n":4,"title":"SpaceXAI - Grok Speech to Text and Text to Speech APIs","url":"https://x.ai/news/grok-stt-and-tts-apis","type":"official","group":"primary","domain":"x.ai"}],"official":4,"filed":"2026-09-29","updated":"2026-09-29","orgs":["xAI","SpaceX"],"title":"xAI releases Grok Voice Think Fast 2.0 speech-to-speech model for voice agents","summary":"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.","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)"],"key_numbers":[],"tags":["xai","grok","voice","speech-to-speech","realtime","voice-agents"],"science":null,"body_md":"## What happened\n\nxAI shipped the second generation of its realtime voice model, which reasons while it talks and can call web search,\nX search, file search and remote MCP tools from inside a voice session. It powers Grok's voice mode, the Grok assistant\nin Tesla cars and Starlink support calls, and is exposed via a WebSocket API that mirrors OpenAI's Realtime protocol.\n\n## Why it matters\n\nIts reported AA S2S Quality Index (82.9) put it roughly level with Google's Gemini 3.8 Live Extended Thinking (82.6,\nSept 2026) and marked xAI's push to compete on voice agents on price. Benchmarks are xAI-reported.","disputed":[],"related":[{"id":"2026-09-21-grok-4-7","url":"https://postcutoff.com/e/2026-09-21-grok-4-7/","date":"2026-09-21","date_precision":"day","short_title":"SpaceXAI releases Grok 4.7 with a new larger base model and new safeguard stack","deck":null,"takeaway":"xAI's rapid 4.x cadence (4.5 -> 4.6 -> 4.7 within months) while Grok 5 remains in training shows the lab competing on price-performance for agentic coding rather than waiting for a single giant release.","category":"model-release","category_label":"Model releases","importance":4,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":4,"official":1,"filed":"2026-09-29","updated":"2026-09-29","orgs":["xAI","SpaceX"]},{"id":"2026-08-12-grok-4-6","url":"https://postcutoff.com/e/2026-08-12-grok-4-6/","date":"2026-08-12","date_precision":"day","short_title":"SpaceXAI releases Grok 4.6, matching GPT-5.6 Sol on the AA Intelligence Index","deck":null,"takeaway":"On 2026-08-12 SpaceXAI (xAI after its merger with SpaceX) released Grok 4.6, a flagship model aimed at long-running agents, coding and knowledge work.","category":"model-release","category_label":"Model releases","importance":4,"confidence":"high","status":{"key":"confirmed","labels":["Confirmed"]},"sources":8,"official":6,"filed":"2026-09-29","updated":"2026-09-30","orgs":["xAI","SpaceX"]},{"id":"2026-07-01-xai-grok-voice-agent-builder","url":"https://postcutoff.com/e/2026-07-01-xai-grok-voice-agent-builder/","date":"2026-07-01","date_precision":"day","short_title":"xAI launches Grok Voice Agent Builder, a no-code platform for phone voice agents","deck":null,"takeaway":null,"category":"product","category_label":"Products","importance":2,"confidence":"medium","status":{"key":"partly","labels":["Partly confirmed"]},"sources":3,"official":2,"filed":"2026-09-29","updated":"2026-09-29","orgs":["xAI","SpaceX"]}],"people":[],"posts":[],"videos":[],"models":[{"id":"grok-voice-think-fast-2-0","name":"Grok Voice Think Fast 2.0","url":"https://postcutoff.com/m/grok-voice-think-fast-2-0/"}],"changes":[{"date":"2026-09-29","type":"edit","text":"Linked the Voice Agent Builder entry (2026-07-01)"},{"date":"2026-09-29","type":"filed","text":"Created"}],"provenance":{"agents":[{"model":"Claude Opus 5.5","maker":"Anthropic","tool":"Claude Code"}],"filed":"2026-09-29","run":null,"sources_read":null,"updated":"2026-09-29","human_review":null,"version":{"date":"2026-10-04"}},"gaps":[{"model_id":"gpt-6-astra","name":"GPT-6 Astra","cutoff":"2026-04","days_after":90,"in_training_data":false},{"model_id":"claude-opus-5-5","name":"Claude Opus 5.5","cutoff":"2026-06","days_after":29,"in_training_data":false},{"model_id":"gemini-4-hydrogen","name":"Gemini 4 Hydrogen","cutoff":"2026-03","days_after":120,"in_training_data":false},{"model_id":"grok-4-7","name":"Grok 4.7","cutoff":"2026-05","days_after":59,"in_training_data":false}],"short_url":null}