Claude Mythos FAQ

Claude Mythos is 'by far the most powerful AI model' Anthropic has ever developed, internally codenamed 'Capybara.' It was accidentally leaked on March 26, 2026 through a CMS misconfiguration. The leaked blog describes it as 'a new name for a new tier of model: larger and more intelligent than our Opus models,' achieving 'dramatically higher scores on tests of software coding, academic reasoning, and cybersecurity.'

According to the leaked draft blog post, Anthropic chose the name 'Mythos' to 'evoke the deep connective tissue that links together knowledge and ideas.' The word also comes from the Greek μῦθος, meaning a foundational narrative that shapes how we understand reality.

Capybara is a brand-new tier in Anthropic's model hierarchy, and Mythos is the first model in that tier. Just as Haiku, Sonnet, and Opus are different tier names, Capybara represents an entirely new level beyond Opus. Mythos is not an Opus upgrade — it is an architecturally distinct new model.

On March 26, 2026, security researchers Roy Paz (LayerX Security) and Alexandre Pauwels (University of Cambridge) discovered that Anthropic's content management system (CMS) was misconfigured, leaving approximately 3,000 unpublished assets publicly accessible. These included draft blog posts, model specifications, and internal development files.

According to leaked internal documents, Anthropic describes Mythos as 'far ahead of any other AI model in cyber capabilities.' It can autonomously discover zero-day vulnerabilities, generate exploit code, and evade detection at speeds 'that far outpace defenders.' Within 24 hours of disclosure, the Global Cybersecurity Index dropped 4.2%, erasing approximately $400 billion in market capitalization.

Anthropic's model family includes four tiers: Haiku (lightweight, fast), Sonnet (balanced workhorse), Opus (flagship reasoning), and Mythos/Capybara (a new tier beyond Opus). Leaked documents show Mythos achieves 'dramatically higher scores' across all core benchmarks, but is also 'very expensive to serve.'

Anthropic confirmed the model's existence. The leaked blog reveals they are 'taking a slower, more gradual approach to releasing Mythos than we have with our other models,' beginning with 'a small number of early-access customers, who will explore the model's cybersecurity applications and report back what they find.' The model is described as 'a large, compute-intensive model — very expensive for us to serve, and very expensive for our customers to use.'

Yes. During Anthropic's Frontier Red Team testing, Mythos independently completed two attacks in 90 minutes: first exploiting a blind SQL injection in Ghost CMS to steal admin API keys, then targeting the Linux kernel and uncovering a stack buffer overflow in the NFSv4 daemon — a bug hidden for roughly 20 years. For context, even Opus 4.6 (not Mythos) discovered 500+ high-severity zero-days in production codebases with no specialized tooling.

Yes, they refer to the same model. However, 'Claude 5.0' is not Anthropic's official name — Anthropic doesn't use numeric versioning. Their models are organized by tier names: Haiku, Sonnet, Opus, and now Mythos. '5.0' is an informal label used by some media outlets. The official name is Claude Mythos, internal codename Capybara.

No. This is an independent, unofficial fan site with no affiliation to Anthropic, PBC. All information is sourced from public media reports and leaked materials, provided for research and informational purposes only. We explicitly distinguish between 'confirmed facts' and 'speculation based on leaked documents.'