The AISI (UK AI Safety Institute, the UK Government body established in November 2023 to evaluate frontier AI capabilities) published its Frontier AI Trends Report on 6 May 2026, confirming that GPT-5.5, OpenAI's frontier language model, cleared the 32-step autonomous cyber attack chain benchmark known as "The Last Ones" (TLO). GPT-5.5 achieved 71.4% on the expert cyber suite and solved the TLO benchmark end-to-end in 2 of 10 attempts. GPT-5.5 is the second model to clear the benchmark; Anthropic's Claude Mythos cleared the same threshold on 1 May 2026 .
AISI's report assesses frontier cyber capability as doubling every four months. The 32-step attack chain benchmark triggered an emergency convening of five Wall Street bank CEOs by Treasury Secretary Bessent and Fed Chair Powell in April 2026, after Claude Mythos became the first model to clear it . Five days after Mythos cleared the threshold on 1 May, GPT-5.5 repeated the result on 6 May.
Two separate frontier models clearing the same benchmark within five days changes the nature of the risk assessment. A single-model capability that is deliberately kept under restricted access (as Mythos Preview was, through Project Glasswing with access limited to twelve partners) can be managed through deployment controls. A benchmark cleared by two models from different organisations within five days of each other is no longer a single-deployment governance question; it is a class of capability that has arrived across the frontier.
AISI's four-month doubling rate, if it holds, means the next iteration of the same benchmark class will be cleared by a broader set of models within months. AISI's evaluation function, confirming which models have crossed which thresholds, is doing the work that no other institution with formal standing has yet stepped in to perform. Whether that evaluation function informs regulatory action in any jurisdiction within a timeframe that is operationally relevant to the doubling rate is the question AISI's report leaves open.
