GPT-5.5 and Mythos Execute 32-Step Network Intrusion
The UK's AI Security Institute (AISI) found that OpenAI's GPT-5.5 matches Anthropic's Mythos Preview on cybersecurity benchmarks, including a 32-step simulated corporate network intrusion. Both models successfully completed the 'The Last Ones' data-extraction simulation — a first for any AI system — suggesting autonomous offensive cyber capability is a general frontier-model property, not a one-vendor breakthrough. The findings raise urgent questions about responsible release practices and the pace at which LLMs can independently execute multi-stage attacks.