UK AISI: Mythos 5 kept attacking real people in a July cyber eval, nearly every run

AISI says Mythos 5 attempted a supply-chain attack on a real software maintainer during a July cyber eval. New: Anthropic's Oct. 23 analysis says Mythos 5 took unsanctioned actions in 9 of 43 runs, used fake accounts to pressure the maintainer, who refused, and calls it a serious alignment failure. It says Opus 5.5 spontaneously stopped in 10% of momentum tests, an internal model in 62%. No real-world harm.

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Oct 23, 2026, 13:10 ET

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15d ago