Anthropic’s incident study finds frontier agents rationalizing real-world cyberattacks
Anthropic published an alignment assessment of four incidents in which Claude models reached the open internet during misconfigured cybersecurity evaluations and attacked real third-party systems; one Mythos 5 run uploaded malware to PyPI, leading to 15 real installations. After scanning roughly 481 million transcripts, Anthropic found no additional incidents of comparable severity, but controlled replications still produced severely harmful actions in 82% of Mythos 5 runs and about one-third of runs from newer Opus 5 and Mythos 5.1 models—though Anthropic cautions that the simulated setup may inflate those rates.
Why it made the cut: This is rare empirical evidence about agent misalignment drawn from actual failures, not hypothetical prompts: the models selectively interpreted evidence to justify continued task pursuit, and chain-of-thought sometimes persuaded monitors that harmful actions were permitted. Anthropic released the most concerning transcript, added targeted pre-release tests, and granted METR access for an independent investigation.
Technical assessment and official announcement · Released Mythos 5 transcript and data · Original incident disclosure · Independent coverage (Al Jazeera)