Anthropic Releases Claude Fable 5, Its First Generally Available Mythos-Class Model

On June 9, 2026, Anthropic released Claude Fable 5, its first generally available Mythos-class model, pairing it with new safety classifiers that flag prompts in dual-use domains such as cyber and bio, plus a fallback mechanism that automatically reroutes refused requests to Claude Opus 4.8. At the same time, the company outlined plans to provide Claude Mythos 5—built on the same base model but with some safeguards removed—on a limited basis to cyberdefenders and infrastructure providers working with the U.S. government via Project Glasswing (announcement).