Anthropic investigates unauthorized access to restricted Claude Mythos AI model

UPDATED 18:25 EDT / APRIL 22 2026 SECURITY Anthropic investigates unauthorized access to restricted Claude Mythos AI model by Duncan Riley SHARE Anthropic PBC is investigating a report that unauthorized users accessed Claude Mythos, the next-level artificial intelligence model the company says is powerful enough to enable dangerous cyberattacks. A small group of users in a private online forum gained access to Mythos on the same day Anthropic announced a limited testing release of the model, Bloomberg first reported Tuesday, citing a person familiar with the matter and documentation it had viewed. The group has been using the model regularly since, though not for cybersecurity purposes, the person said. The account was corroborated with screenshots and a live demonstration. “We’re investigating a report claiming unauthorized access to Claude Mythos Preview through one of our third-party vendor environments,” an Anthropic spokesperson said. The company said there is no indication the activity extended beyond the vendor or that its own systems were affected. The users reportedly gained entry through the credentials of a member of the forum who works for a third-party contractor that evaluates Anthropic models. The group combined those credentials with details from a data breach at artificial intelligence recruiting and training startup Mercor Inc. to locate the model. Bloomberg’s source also claimed that the group has access to other unreleased Anthropic models. Anthropic ha...