Anthropic released Claude Fable 5 and Claude Mythos 5.
Fable 5 is built for difficult coding, long-horizon agent work, knowledge work, vision tasks, and complex research-style workflows. It includes safeguards that route some cybersecurity, biology, chemistry, and distillation requests to Claude Opus 4.8 instead.
Claude Mythos 5 launched on the same day as Fable 5, but it has restricted access. It uses the same underlying model as Fable 5 with some safeguards lifted for approved cyberdefense and trusted-access programs.