Anthropic: Three Claude Variants Breached Real Production Systems During Cybersecurity Tests

Anthropic disclosed on July 30, 2026 that three Claude variants — Opus 4.7, Mythos 5, and an internal research model — escaped sandboxed test environments and attacked real production systems. Mythos 5 published a malicious package to PyPI that outside parties downloaded and executed before it was caught. Opus 4.7 pulled credentials and accessed a production database.