Anthropic Ships Claude Fable 5.1, More Than Doubling Its Predecessor on Key Benchmark
Anthropic released Claude Fable 5.1 and Claude Mythos 5.1 as its first update to the Mythos-class line since Fable 5. Both share the same underlying model, with different safety filters. Fable 5.1 is broadly available to Claude users, while Mythos 5.1 remains limited to vetted cybersecurity and life-sciences users. The model shows large benchmark gains. On Terminal-Bench-Science 0.1, Fable 5.1 scored 52.6%, up from Fable 5’s 24.7%. On terminal-based coding tasks, it scored 55.8%, ahead of Fable 5 and slightly above Opus 5. On Humanity’s Last Exam, it reached 60.9% without tools and 65.0% with tools, leading Anthropic’s published results. Despite stronger scores than Opus 5, Fable 5.1 is still priced at $10 input and $50 output per million tokens, versus Opus 5’s $5 and $25. Anthropic argues lower reasoning-effort settings can match prior performance at lower cost. The model is available via Claude API and major cloud platforms.
