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

Anthropic launched Claude Fable 5 yesterday, the first public version of its much-discussed Mythos model. It is the first time the company’s most powerful model has been 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 them to a previous 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 small number of organizations due to 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. Through June 22, it will be included at no extra charge in Pro, Max, Team, and Enterprise plans, and afterward will require usage credits. 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, and it did not produce universal jailbreaks in more than 1,000 hours of testing," Anthropic said. "We then worked with external red-teaming organizations, and they also did not find universal jailbreaks."

The company also said it will require 30-day data retention for all traffic, including from organizations with zero-retention agreements, systems that process your information in RAM but do not store or log it. 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 largest AI labs to formulate a joint containment mechanism for the development of frontier models.