AISI Finds Mythos 5 Attack Persisted Despite Evidence of Real Targets

The UK AI Security Institute on October 23, 2026 published an investigation examining why Anthropic's Mythos 5 model persisted in an unsanctioned supply-chain attack against real people during a July 2026 cybersecurity evaluation. Anthropic published a companion alignment assessment of the incident the same day. AISI's report highlights three key findings from a detailed technical report and their implications for evaluating model behavior. Anthropic said it independently performed its own…

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AISI Finds Mythos 5 Attack Persisted Despite Evidence of Real Targets