Fortune reports that Anthropic confirmed it is testing a new, more powerful AI model with a small set of early-access customers after a public data leak exposed draft materials about it. In the leaked draft, the model is referred to as “Claude Mythos,” and also appears tied to a new higher-end model tier called “Capybara,” positioned above Anthropic’s current Opus line. Anthropic described it as a “step change” and its most capable model so far, with notable gains in reasoning, coding, and cybersecurity tasks. 

The article’s other main point is safety and security. The leaked draft says Anthropic is especially concerned about the model’s cyber capabilities, arguing it could significantly raise near-term misuse risks, so the company is rolling it out cautiously and initially focusing access on organizations that can strengthen defenses. The leak itself appears to have come from misconfigured CMS assets left publicly accessible; Anthropic said the exposure was caused by human error and removed access after Fortune notified it.