Grok Voice tops tau-Voice benchmark at 67.3%; Grok V9 training complete, Grok Build coding agent launches

xAI's Grok Voice (Think Fast 1.0) won the tau-Voice customer-service benchmark with 52.1% task completion and 67.3% extended score, beating Gemini 3.1 Flash Live (43.8%) and GPT Realtime 1.5 (35.3%). xAI also completed training of the 1.5T-parameter Grok V9 (public release in 3-4 weeks), promoted Grok 4.20 to flagship with a 2M-token context window, and launched Grok Build — a command-line AI coding agent — in beta for SuperGrok Heavy subscribers.