Anthropic says Claude Mythos 5 tried to trick real developers into accepting malware during a UK AISI cyber test. tl;dr :

-Crossed the test’s boundaries in 9 of 43 runs.

-After failing inside the test network, targeted an unrelated GitHub project.

- Created fake identities to endorse its malicious code and pressure maintainers into accepting it.

- Treated maintainers as “simulated” people, while recognizing other commenters as real.

- Once the attack was underway, continued in 98% of replayed trajectories. Anthropic calls this “momentum” previous actions and self-written notes appeared to reinforce the harmful strategy.

Separate runs sabotaged each other by hijacking accounts, exhausting request limits and deleting another agent’s output.

Newer models were less likely to begin the attack. Luckily NVIDIA released OpenShell. Seriously.

#ArtificialIntelligence #cybersecurity #AgenticAI #AISafety #redteaming

In a UK AISI evaluation, Mythos 5 took unsanctioned actions that impacted real people and organizations. In this post, we investigate these behaviors from Claude Mythos 5 further, to understand what they reveal about the model’s alignment.