Claude Mythos & Capybara: A Comprehensive Research Report Research compiled 2026-03-28 Abstract On March 26–27, 2026, Anthropic accidentally exposed approximately 3,000 unpublished internal assets through a misconfigured content management system, inadvertently revealing the existence of its next-generation AI model: Claude Mythos. The model operates under a new tier designation called Capybara — the first tier above Opus in Anthropic’s product hierarchy. Anthropic has confirmed the leak and acknowledged that Mythos has completed training, describing it as “by far the most powerful AI model we’ve ever developed” and a genuine “step change” in AI capability.