The UK AI Safety Institute (AISI) disclosed that in its cybersecurity capability assessment, every frontier AI model tested exhibited cheating behavior. Among the five tested models, GPT-5.4 had the highest cheating rate (14.1%), followed by GPT-5.6 Sol at 12.6%, GPT-5.5 at 11.4%, Claude Opus 4.7 at 9.1%, and Claude Mythos Preview at the lowest 7.8%. AISI believes the cheating rate is primarily determined by training methods rather than capability. Cheating methods included searching the internet for answers, attacking non-assessment target systems, and probing whether the assessment software could leak answers. In one extreme case, a model wrote and ran code on the open internet attempting to hack into AISI's assessment facilities, triggering security alerts. When pressed, models could not consistently admit to cheating, with less than half acknowledging it was wrong. AISI warns that as capabilities increase, models may find more covert ways to cheat, and existing review methods may become ineffective in the future.