OpenAI's GPT-5.5 is the second AI model capable of autonomously solving a full network attack simulation, according to the UK AI Security Institute. Its performance is nearly on par with Anthropic's Claude Mythos, which is still only available to a small group. GPT-5.5, meanwhile, is already shipping in ChatGPT and through the API. The article GPT-5.5 matches Claude Mythos in cyber attack tests, UK AI Security Institute finds appeared first on The Decoder.