Claude Fable 5.1 is generally available on AWS and brings Anthropic’s most capable frontier model to all customers. Fable 5.1 delivers frontier intelligence for ambitious tasks across coding, scientific research, and enterprise workflows. A clear improvement over Claude Fable 5, Fable 5.1 is a step up in intelligence on the hardest reasoning tasks, providing better judgement on ambiguous work and fewer confident wrong answers. Claude Mythos 5.1, the same underlying model as Claude Fable 5.1 with its full cyber and bio capabilities retained for cybersecurity and biology research, is available with limited access.

Claude Fable 5.1 is built for long-running, high-stakes work that runs for hours and spans many applications. It can own more of a software project on its own, handling features across an entire codebase, code review, and performance work over sessions that run for hours. If it gets stuck, it says so instead of reporting success, and it is less likely to take shortcuts like disabling a failing test. It takes analysis from the first question to the finished document, and it is Anthropic’s strongest model yet for knowledge work.

Anthropic has designated Fable 5.1 a Covered Model, a category of Claude models that carry additional data retention, safety review, and access policies wherever they’re offered. Enterprise Frontier Safeguards (EFS) built in partnership between AWS and Anthropic, will let eligible customers use Covered Models while keeping their data in a cloud environment they control. Read the launch blog to learn more.

Customers have two ways to access Claude Fable 5.1: Amazon Bedrock and Claude Platform on AWS. To learn more, see the Amazon Bedrock documentation, regional availability, and Claude Platform on AWS documentation..