UK AISI finds Claude Mythos Preview can autonomously take over a simulated corporate network
UK AISI found Claude Mythos Preview completed a 32-step corporate-network takeover in three of ten attempts; Anthropic later verified practical downstream impact through large-scale real-world vulnerability discovery.
TOWARD DOOM55confidence 90/100
Why it moved the index
Independent testing demonstrated end-to-end autonomous compromise across a long simulated attack chain, while later real-world vulnerability discovery verifies practical impact. Magnitude is limited because the range was weakly defended and simulated.
AUDIT TRAIL
Assessment history
- R1Toward 55 · confidence 90
New historical model-specific autonomy result paired with separately dated practical cyber-impact evidence.
11 Aug 2026