Anthropic released Claude Fable 5.1 and Mythos 5.1. The watermark exists because of the EU AI Act, and its detection API goes only to eligible groups.

In June, Anthropic first released Fable 5, its Mythos-class AI model for Claude. Three months later, Anthropic is enhancing Claude...

Anthropic releases Claude Fable 5.1 broadly and Mythos 5.1 to vetted Project Glasswing users, with 1M token context and reduced cache costs.