Claude Fable 5.1 Official ReleaseProvider report
2026-09-01Based on the complete main comparison table on Anthropic's official September 1, 2026 Claude Fable 5.1 / Mythos 5.1 release page. The compound OSWorld 2.0 partial / strict and Humanity's Last Exam no-tools / with-tools cells are split into nine metrics, producing 32 available scores; em-dash cells do not create scores. Claude Mythos 5.1 and Fable 5.1 are the same model, so no separate model is created. The 60.9% Mythos 5.1 mode result on Terminal-Bench 4.0 is retained in raw.merged_mode_values, while the public Fable 5.1 result of 55.8% is the primary score. OSWorld 2.0 uses the August 2026 task release and is not directly comparable with earlier releases.