Very interesting evaluation from the UK’s AI Security Institute of the not yet publicly available Claude Mythos Preview. On the happy side, …

Very interesting evaluation from the UK’s AI Security Institute of the not yet publicly available Claude Mythos Preview. On the happy side, in its current form, Myth is nowhere near as scary as Tom Fridman (who worries about schoolchildren accidentally taking down power grids) and others made it out to be. On the darker side, it really does arm attackers to a greater degree than Mythos’s predecessors. A key part that gives a little bit of comfort is that (for the most part?) the only system under immediate threat are those that are small, weakly defended and vulnerable. One hopes that by now no mission-critical infrastructure is “small, weakly defended, and vulnerable” with ready network access. One hopes. But even if Mythos was somewhat oversold in the media, the time to get our cybersecurity house in order is now (or better yet last year) — especially given the sudden profusion of agent-written code that may in fact be both weakly defended and vulnerable. We conducted cyber evaluations of Claude Mythos Preview and found that it is the first model to complete an AISI cyber range end-to-end. 🧵

Source: Gary Marcus (X) | 2026-04-13