Unknown Group Allegedly Accesses Claude Mythos, Anthropic Investigates Security Hole

Anthropic says an unknown group accessed Claude Mythos—an unreleased, highly restricted model—via a third‑party vendor environment. Bloomberg reports, citing a live demo and screenshots, that the group used data from a Mercor breach and other intel to pinpoint Mythos and has been experimenting with it since April 7. The group claims no malicious intent, but Anthropic is investigating the breach and the security hole remains a concern.