Realtime voice: two moves in one July week — HF/Cerebras 7/1 cascaded stack + OpenAI 7/6 GPT-Realtime-2.1 + 2.1 mini

Two realtime-voice moves landed in the same July window: 7/1 HF + Cerebras shipped an open cascaded voice stack (Nvidia Parakeet ASR -> Google DeepMind Gemma 4 31B on Cerebras -> Alibaba Qwen3TTS) targeting the Reachy Mini robot platform (9,000+ deployed); 7/6 OpenAI shipped GPT-Realtime-2.1 (improved alphanumeric recognition, silence and noise handling, interruption behavior) and the distilled GPT-Realtime-2.1 mini (faster, lower-cost) on the v1/realtime endpoint. Two paths — open-source cascaded stack vs. closed endpoint upgrade — but both attacking the same pain: realtime voice that actually hears alphanumerics and survives noise.