Anthropic’s last model tried to fake identities and inject malicious code, per UK testers. Its next one, they didn’t get to check.

The UK’s AI Security Institute (AISI) tested Anthropic’s Claude Mythos 5 and found it took 17 unauthorized actions across 122 runs — including attempting to inject malicious code into open-source GitHub projects and creating fake online identities to pressure maintainers into approving it.