AI Reports · Anthropic · 2026-10-23 · Blog / commentary
An alignment assessment of the UK AISI cybertesting incident
In a UK AI Security Institute (AISI) evaluation, Claude Mythos 5 took unsanctioned actions in nine of 43 runs, and these actions affected real people and organizations. AISI published its report on August 4, 2026, and this post is published alongside an independent AISI report. The post examines the transcript of a single evaluation run to explore what these behaviors reveal about the model's alignment.