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AISI tested a newer Mythos Preview checkpoint (reported 2026-05-13)

2026-05-13 · 18:45 UTC ·@daniel_mac8 ·1 min read

Brief

Daniel Mac (@daniel_mac8) reports AISI's 2026-05-13 tests of a Mythos Preview checkpoint solved a 20‑hour task ('The Last Ones') 6/10 times and the previously unsolved industrial 'Cooling Tower' 3/10 times. He notes cyber time-horizon progress accelerated (8 months → ~4.7 months), says Mythos and GPT-5.5 exceeded the trend, and argues this signals a long‑horizon autonomy takeoff not confined to cyber.

Why it matters

AISI tested a newer Mythos Preview checkpoint (reported 2026-05-13): it solved "The Last Ones" (a 20‑hour task) in 6/10 attempts and solved the previously unsolved industrial-control "Cooling Tower" task in 3/10 attempts (AI Security Institute confirmed).

Key details

  • Cyber task time-horizon progress accelerated from a doubling every ~8 months to every ~4.7 months; both Mythos and GPT-5.5 exceeded that trend, which the author frames as potential super-exponential capability growth.
  • The author claims this indicates long-horizon autonomous capabilities have crossed a threshold, notes Anthropic allowed organizations to test cyber autonomy first, and warns there is no obvious reason such capabilities would remain confined to cyber — "We are in the takeoff."
Source evidence

🚨 BREAKING: AISI tested a newer Mythos Preview checkpoint.

These numbers are insane:

> solved "The Last Ones", a 20hr task, in 6/10 attempts
> solved the previously unsolved "Cooling Tower" task in 3/10 attempts
> cyber task time horizons went from doubling every 8mos to every ~4.7mos
> Mythos and GPT-5.5 both exceeded that trend

This could be a super-exponential if the trend holds.

Ignore the people who say: "It's just better at hacking."

It looks like long-horizon autonomy crossing a threshold.

Cyber just happens to be the domain where Anthropic allowed organizations to test it first.

There is no obvious reason to assume this stays confined to cyber.

We are in the takeoff. You can feel it.

AI Security Institute (@AISecurityInst)

Mythos Preview also solved "Cooling Tower", our industrial control system range, in 3 of 10 attempts.

— https://nitter.net/AISecurityInst/status/2054589766490825081#m