Anthropic’s Fable 5.1, released September 1, currently leads verified Humanity’s Last Exam leaderboards at 65% as of mid-October 2026, ahead of Opus 5 (64.7%) and Mythos 5 (64.5%), building on Fable 5’s June 2026 debut that first swept major benchmarks including HLE with tools. Leaks from early September point to a 5.2 or 5.5 variant from a new pretraining run targeted for late September or early October, though Anthropic has so far only confirmed Sonnet and Haiku 5.5 releases without mentioning another Fable. Traders are watching for whether this next model becomes the first 5.2+ variant to claim the top HLE spot amid tightening competition from Opus 5.5 variants that have posted higher scores on some Artificial Analysis HLE runs. Resolution hinges on official model cards or independent evaluations confirming a new record before year-end deadlines.