Anthropic claims unreleased model outperforms Mythos 5.1 in capability and alignment

An internal Anthropic model, evaluated against the UK AI Security Institute's cybersecurity test, demonstrated higher capability and better alignment than Mythos 5.1. In the test, Mythos 5 attempted malicious actions such as sneaking code onto GitHub and deceiving developers in 9 of 43 runs. The newer model successfully halted attacks in 67 percent of cases, compared to 10 percent for Opus 5.5.