Anthropic today introduced Claude Fable 5, a Mythos-class model that is safe to use, and is introducing Claude Mythos 5 to a small group of security and infrastructure providers with some suggested protections.
Legend 5 has safeguards that can prevent its cyber security capabilities from being misused. Protection ensures that questions on specific topics will be answered by Claude Opus 4.8. Meanwhile, Mythos 5 will be distributed through the company’s Project Glasswing as an upgrade to the Mythos preview. The company says this new model has the strongest cybersecurity capabilities of any model. A trusted access program will be running soon for the Mythos 5 expansion.
In his blog announcement, Anthropic wrote: “The capabilities of models like Fable 5 and Mythos 5 have the potential to do the best in the world. We saw the beginning of this in Project Glasswing, where models helped cyber defenders protect critical software. We also saw it in life sciences research, where models put forward new ideas for prediction and acceleration.”
The new models have been shown to run more smoothly than any of Claude’s previous models, the company wrote. For software engineers, Anthropic reported that Fable 5 “compressed months of engineering into days.” In their tests, they said that a Ruby codebase of 50 million lines was migrated in a day, which would have taken the entire team more than two months to complete by hand. Advanced modeling skills also extend to cognitive function, perception, memory, and life science research.
“Legend 5 is a real step forward for GitHub developers,” said a GitHub spokesperson. “In our initial tests, complex, long tasks were taken with a level of autonomy and reliability that exceeded previous measurements. But what we are most excited about is the guidance
points: a future where developers can delegate tasks to agents and trust results throughout the software lifecycle.”
Mythos 5 and Mythos 5 are offered at $10 for billions of input tokens and $50 for millions of output tokens—less than half the price of the Claude Mythos Preview. Today’s joint launch is another step towards our goal of bringing advanced AI capabilities to as many users as possible, as quickly and safely as possible.
The company also adds data privacy protections, such as personal login to data, and guarantees that data will be deleted after 30 days, in most cases.
Availability
While Claude Fable 5 is available everywhere today, Mythos 5 is limited to Glasswing partners, and some cyber protections have been removed. Developers can use claude-fable-5 through the Claude API.
The scheduled release of subscription plans is as follows, per company:
- From today until June 22, Fable 5 is included in the Pro, Max, Team, and Enterprise plans based on the chair at no additional cost.
- On June 23rd, we will remove Fable 5 from those plans. Using it after that will require usage credits. If the capacity is acceptable, we will expand the installed window.
- After this point—when sufficient volume allows us to do so—we intend to reinstate Legend 5 as a regular part of subscription plans. We aim to do this as soon as possible.
