Anthropic releases Claude Fable 5 and Mythos 5 with major gains in coding and science

Anthropic ships two new models, Claude Fable 5 and Mythos 5, that claim to blow past the current Opus generation, especially in coding and research. Fable 5 finished a code migration for Stripe in one day that would have taken a team two months.

Both models share the same base model. Fable 5 ships with conservative safety guardrails for general use. Mythos 5 drops those restrictions in areas like cybersecurity and is reserved for a small group of partners. Anthropic says Fable 5 beats every generally available model the company has ever shipped and claims state-of-the-art results in nearly all benchmarks tested. The gap widens on long, complex tasks, the company states. On SWE-Bench Pro, a benchmark for solving real software engineering tasks from public GitHub repos without help, Fable 5 hits 80.3 percent. Claude Opus 4.8 lands at 69.2 percent, GPT 5.5 at 58.6 percent, and Gemini 3.1 Pro at 54.2 percent. On Cognition’s FrontierCode benchmark, which tests demanding coding tasks under production standards, Fable 5 scores 29.3 percent. Claude Opus 4.8 manages 13.4 percent. GPT 5.5 gets just 5.7 percent. Fable 5 is also more token-efficient than earlier Claude models, Anthropic claims. At medium effort, it posts the top score among all frontier models on FrontierCode. Payment processor Stripe says Fable compressed five months of engineering work into days. In a Ruby codebase with 50 million lines, the model finished a migration in one day that would have taken a full team over two months. Knowledge work, vision, and long-term memory jump ahead Fable 5 also tops the charts on complex analytical tasks, according to Anthropic.