Anthropic Releases Its “Most Dangerous” Model, But Calls It Fable and Makes It Safer

Anthropic launched Claude Fable 5 yesterday, the public release of its much-discussed Mythos model. For the first time, the company’s most powerful model is available to the public.

The company said the model excels at software engineering, knowledge work and computer vision, but operates under strict safety restrictions. In high-risk areas such as cyber, biology, chemistry and distillation, the model blocks responses and routes users to an earlier model, Claude Opus 4.8. According to Anthropic, these are rare cases, and early data show that at least 95% of Fable activations run fully on the model itself.

Mythos was launched in a limited format in April and was available to only a handful of organizations because of security concerns. Last week, access was expanded to hundreds of organizations in 15 countries, with an emphasis on organizations that manage critical infrastructure. The public version is now available through Claude’s API and Enterprise plans. Until June 22, it will be included at no additional cost in the Pro, Max, Team and Enterprise plans, and afterward it will require usage credits. At the same time, Mythos 5 is also being distributed to organizations that have already been approved for access to the advanced model.

“Internally, we ran an external bug bounty program, where ‘white hat’ hackers try to find security vulnerabilities, for more than 1,000 hours of testing without producing any universal jailbreaks,” Anthropic said. “We then worked with external red-teaming organizations, which also did not find any universal jailbreaks.”

The company also announced that it will require 30-day data retention for all traffic, including from organizations with zero-retention agreements. According to the company, the information will not be used for training, only to defend against new attacks and identify false positives.

The price of Fable 5 and Mythos 5 is $10 per million input tokens and $50 per million output tokens, double the price of Opus 4.8. The launch comes as the company prepares for a stock market listing, alongside OpenAI and Elon Musk’s SpaceX, and shortly after it called on the world’s major AI labs to formulate a joint containment mechanism for the development of frontier models.