Story · @claudeai
Anthropic introduces Claude Fable 5.1 and Claude Mythos 5.1 (@claudeai)
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Anthropic released Claude Fable 5.1 and Claude Mythos 5.1, reporting 55.8% on Terminal-Bench 4.0 against 42.0% for Fable 5, with cache reads priced 75% below Fable 5. Fable 5.1 is available everywhere today, while Mythos 5.1, aimed at cyberdefenders and life scientists, goes through trusted-access programs.
In plain words
- Anthropic released Claude Fable 5.1 widely and limited Claude Mythos 5.1 to approved-access programs.
- Anthropic says Fable 5.1 scored 55.8% on Terminal-Bench 4.0, a coding test, versus Fable 5's 42.0%.
- Reusing previously processed information costs 75% less than with Fable 5, lowering the price of repeated work.
- Mythos 5.1 is aimed at cybersecurity defenders and life scientists, with access limited to trusted programs.
- Developers may spend less on repeated work, while Anthropic controls who can use Mythos in specialized fields.
Appeared in
- Anthropic's deliberately misaligned model, Fable 5.1, and a fix for reward hacking
Sep 02, 2026 · from X
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