Introducing Claude Fable 5.1 and Claude Mythos 5.1

Claude Fable 5.1 and Claude Mythos 5.1 are advanced models for coding and knowledge work, sharing the same underlying architecture while featuring different safety levels. Fable 5.1 is generally available, whereas Mythos 5.1 is restricted to trusted access programs with specialized safeguards for cybersecurity and the life sciences. Alongside these releases, pricing is lowered by roughly twenty-five to forty-five percent for typical and agentic workloads through reduced cache read fees. A new privacy system called Enterprise Frontier Safeguards will store customer data in cloud infrastructure controlled entirely by the user.

Both models set new performance standards in problem-solving, terminal coding, and multidisciplinary reasoning while reducing false positives in safety filters. In scientific testing, Mythos 5.1 successfully designed high-affinity protein binders with hit rates reaching nearly fifty percent across multiple targets, and it optimized open-source deep learning models to run up to 2.5 times faster while reducing computational costs. Additionally, Fable 5.1 processed NASA Magellan radar data to create a high-resolution elevation map of a third of Venus, revealing details down to two to three kilometers.

These models matter because they demonstrate how artificial intelligence can reliably handle complex, long-running tasks, accelerate software debugging, and contribute directly to scientific progress in biology and planetary research.