Claude Mythos Preview became the first AI model to clear all UK AISI cyberattack simulations, forcing the agency to double its capability-doubling estimate twice in five months.

Anthropic's Claude Mythos Preview cleared all cyberattack simulations from the UK AI Security Institute (AISI) — the first model to do so. The milestone forced AISI to revise its estimate of AI cyber capability doubling time from 8 months in November 2025 to 4.7 months by February 2026.

Key facts

Claude Mythos cleared all AISI cyber ranges — first model to do so.

AISI revised capability doubling time from 8 to 4.7 months in five months.

Mythos completed 32-step attack in 6 of 10 attempts.

Solved 'Cooling Tower' simulation no prior model passed.

XBOW found 42% false negative reduction vs Opus 4.6.

The capability acceleration

AISI's cyber ranges simulate complex multi-step attacks. One range models a 32-step corporate network intrusion that human experts need about 20 hours to complete, according to AISI.…