Claude Fable 5.1

Claude Fable 5.1 is a proprietary language model from Anthropic, released on Sep 1, 2026.

At $10 input and $50 output per million tokens, it ranks #30 of 33 for input price, placing it among the higher-priced models tracked here.

Its context window of 1.0M tokens ranks #6 of 34 for context depth in this dataset.

It targets coding, agents, reasoning, research workloads.

Released Sep 1 2026 alongside Claude Mythos 5.1 (same underlying model, restricted-access safeguards for vetted cybersecurity/life-sciences organizations via Anthropic's Cyber and Life Sciences Verification Programs). Anthropic recommends it over Opus 5 for demanding reasoning and long-horizon agentic work, or when Opus 5 at higher effort still falls short. Anthropic's own comparison shows it beating Fable 5 and Opus 5 on every benchmark listed above except Terminal-Bench 4.0, where sibling model Mythos 5.1 (not Fable 5.1) posts the top score. API identifier claude-fable-5-1, reliable knowledge cutoff June 2026, retirement not sooner than Sep 1 2027.