GPT-5.5 Edges Mythos in Cyber Eval

This is less a brag about benchmark vanity and more a warning that frontier models are now compressing expert cyber workflows into minutes. The real story is the speedup: once agents can chain tools, reason through multi-step tasks, and operate cheaply, both defenders and attackers get a materially different cost curve.

• –AISI’s writeup puts GPT-5.5 ahead of Mythos Preview, GPT-5.4, and Opus 4.7 on expert-level cyber tasks, but the margin is small; the bigger signal is how high the ceiling already is.
• –The 12-hour-to-10-minute gap matters more than the exact pass-rate delta because it shows how quickly model-assisted exploit research can scale.
• –NCSC’s companion guidance is consistent with this trend: defenders should assume attackers can already use capable AI and should adopt the same tools for detection, patching, and remediation.
• –This is still a simulated evaluation, not proof of real-world end-to-end compromise at scale, but it strongly suggests security teams need stronger monitoring and faster response loops now.