Claude creator Anthropic is developing a new AI model called Claude Mythos, described internally as the company’s most capable model to date, with draft materials about the system being leaked online this week.
“We’re developing a general purpose model with meaningful advances in reasoning, coding, and cybersecurity,” an Anthropic spokesperson told Fortune. “Given the strength of its capabilities, we’re being deliberate about how we release it. As is standard practice across the industry, we’re working with a small group of early access customers to test the model. We consider this model a step change and the most capable we’ve built to date.”
“Mythos is a new name for a new tier of model: larger and more intelligent than our Opus models—which were, until now, our most powerful,” Anthropic wrote. “We chose the name to evoke the deep connective tissues that link together knowledge and ideas.”
According to Anthropic, Mythos scored “dramatically higher” than Claude Opus 4.6 on tests of software coding, academic reasoning, and cybersecurity.
The leak of Mythos appears to have originated from draft materials stored in an unsecured content management system. According to Fortune, Anthropic restricted public access to the data store after being notified that the files were searchable online. The company attributed the exposure to human error in the configuration of its CMS tools.
However, Anthropic’s documents labeled Mythos as version one of the new model, and described version two internally as “Capybara,” which the company also positioned above its current top-tier Opus models.
The draft materials also highlighted concerns about the system’s potential cybersecurity implications.
“Although Mythos is currently far ahead of any other AI model in cyber capabilities, it presages an upcoming wave of models that can exploit vulnerabilities in ways that far outpace the efforts of defenders,” the company wrote.
Because of those risks, the company said it plans to release the model cautiously, beginning with a limited early-access rollout aimed at organizations working on cybersecurity defense.
Anthropic did not immediately respond to Decrypt’s request for comment.
While Anthropic took down the blog post, news of the leak quickly spilled into financial markets.
That sell-off erased roughly $285 billion in market value as investors reassessed the long-term impact of AI agents on enterprise software businesses.
"The market's response was a signal, not that AI agents will immediately replace these businesses, but that investors are finally pricing in the structural risk that foundation model providers can now compete directly with the software layer," Nexatech Ventures founder Scott Dylan told Decrypt at the time. “That's a polite way of saying if Anthropic can build a legal workflow tool in-house, what's stopping them from doing the same for finance, procurement, or HR?”
