THE CLAIM. OpenAI and Cerebras say GPT-5.6 Sol in Ultrafast mode hits up to 750 output tokens per second, 11x faster than Fable 5, and blitzed all 2,500 Humanity's Last Exam questions in 11 hours 11 minutes against Fable 5's 78 hours 27 minutes, with no quality compromise.

THE CHECK. the silicon is plausible and the framing is theater. Answering 2,500 independent questions is an embarrassingly parallel workload, so the wall-clock race measures cluster scale, not model speed, and per-question latency is not disclosed. Neither company states that Ultrafast performs identically to regular Sol, a sentence they would shout if they could write it, and the industry's record on 'no quality loss' serving modes is poor. No price, no context limit, no configuration. The fine print concedes results may vary by workload and configuration.