The UK AI Security Institute says GPT-5.5 cybersecurity simulation results now look a lot less like a one-off milestone and a lot more like a repeatable frontier capability. In its latest evaluation, AISI found that an early checkpoint of OpenAI’s GPT-5.5 reached roughly the same level as Anthropic’s Mythos Preview on hard cyber tasks—and slightly beat it on one key benchmark. That matters because AISI was explicitly testing whether Mythos Preview’s earlier result was a weird outlier. Instead, a second model from a different developer now lands in the same range, including solving a difficult multi-step cyber attack simulation end-to-end in some attempts. If you’ve been tracking rising AI cyber capabilities , this is the part worth circling. GPT-5.5 Cybersecurity Simulation Is No Longer a One-Model Fluke AISI’s headline finding is simple: GPT-5.5 reached a similar cyber capability level to Mythos Preview . That is the interesting result.…