Anthropic releases Claude Fable 5, its first broad release from the Mythos class of AI models, with new safeguards to limit high-risk responses

Anthropic announced Claude Fable 5, described as the most powerful model it has ever made widely available, showing exceptional performance in software engineering, knowledge work, and vision, with its lead over other models growing as tasks become longer and more complex.

Fable 5 uses safeguards that block responses in specific high-risk areas (cybersecurity and biology), falling back to Claude Opus 4.8 when triggered; in testing, 95 percent of Fable sessions ran entirely on Fable responses without falling back. Anthropic also released Claude Mythos 5—the same underlying model but with safeguards lifted in some areas—with access currently limited to organizations in the private Project Glasswing initiative.

Pricing for both models is $10 per million input tokens and $50 per million output tokens—double the rates for Claude Opus 4.8, though half what users pay for Mythos Preview.