Anthropic disclosed that a small group of unauthorized users gained access to its newly released Claude Mythos model on the day the company announced a limited rollout. According to Bloomberg, the intruders guessed the model’s online location using details leaked from a prior breach at data‑training firm Mercur and insider knowledge from a contractor who had evaluated Anthropic’s models. Anthropic said it is investigating the incident and reviewing its monitoring systems, which were designed to log and track model usage. The breach, described by security researchers as a standard “educated guess” attack rather than a sophisticated exploit, did not appear to target the model’s advertised cybersecurity capabilities. The episode raises questions about the robustness of Anthropic’s security controls for a product it has marketed as a “watershed moment” for defending digital infrastructure. Read more →