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Achin Bansal
Achin Bansal

Posted on Originally published at gridthegrey.com

Frontier LLMs Now Autonomously Breach Corporate Networks in AISI Cyber Tests

Forensic Summary

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.


Read the full technical deep-dive on Grid the Grey: https://gridthegrey.com/posts/frontier-llms-now-autonomously-breach-corporate-networks-in-aisi-cyber-tests/

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