Claude Fable 5 is the publicly available version of Anthropic's Mythos 5 model, fitted with safety guardrails. In Stripe testing, it reportedly migrated a 50-million-line codebase in a day, compressing months of engineering work. It can rebuild web app source code from screenshots and read scientific charts. On a real-world coding benchmark, it beat GPT-5.5 and Gemini on scores.