Anthropic

We're introducing Claude Fable 5.1 and Claude Mythos 5.1. They're the world's most advanced models for coding and knowledge work, and their research capabilities offer an early glimpse of how AI models will contribute to scientific progress. Claude Fable 5.1 and Claude Mythos 5.1 are the same model, but with different levels of safeguards. Fable 5.1 is generally available, while Mythos 5.1 is available only through trusted access programs; its safeguards are designed to support work in cybersecurity and the life sciences. Fable 5.1 also addresses customer feedback on price, data retention, and safeguards. Typical token-billed workloads are estimated to cost about 25% less than Fable 5 because cache-read prices are lower, with savings up to about 45% on highly agentic work. Enterprise Frontier Safeguards (EFS) aims to give customers ZDR-like privacy while monitoring for misuse, with data stored in customer-controlled cloud infrastructure; until EFS rolls out later this fall, eligible customers can use Fable 5.1 with zero data retention. Cybersecurity safeguards now block 60% fewer false positives, and Fable 5.1 can be used to discover software vulnerabilities (but not develop exploits).