Anthropic releases its first Mythos-class model Claude Fable 

Anthropic just announced Claude Fable 5, a new AI model it said is the most powerful model it has ever made widely available.

According to the company, Fable 5 “shows 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 marks the first broad release from Anthropic’s Mythos class of AI models, after the company said the family was so capable at cybersecurity tasks that it was too dangerous to release publicly. Anthropic said the release was “made possible by new safeguards that block responses in specific high-risk areas,” with the system falling back to Claude Opus 4.8 — a model it praised for “honesty” when it launched last month.

Anthropic singled out cybersecurity and biology as two domains where the safeguards may block responses, both areas widely considered sensitive topics for advanced AI systems. The company said that in testing, 95 percent of Fable sessions ran entirely on Fable responses, without falling back to Opus 4.8.

The company is also releasing Claude Mythos 5, but provided few details on what that means. In a blog, Anthropic said Mythos 5 is the same underlying model as Fable 5, “but with the safeguards lifted in some areas.” For now, access appears limited to the steadily expanding group of organizations granted access to Claude Mythos Preview through Anthropic’s — not entirely watertight — private Project Glasswing initiative. Those users will be able to upgrade to Mythos 5, Anthropic said, adding that it plans to “expand access over time through a more systematic trusted-access program.”

Anthropic did not respond on the record to The Verge’s request for comment explaining how either model relates to Claude Mythos Preview or why the models are numbered “5” when there do not appear to be any previously released Mythos or Fable models.

Pricing for both models is significantly higher than its former flagship model — double rates for Claude Opus 4.8, though it’s half what users pay for Mythos Preview — at $10 per million input tokens and $50 per million output tokens, Anthropic said.