Anthropic's Most Powerful AI Ever Just Leaked — Meet Claude Mythos (Codenamed 'Capybara')
March 27, 2026 · 6 min read
Fortune and CoinDesk confirmed: Anthropic accidentally exposed ~3,000 unpublished assets including draft documents about a new model called "Claude Mythos" — internally codenamed "Capybara". Anthropic has confirmed the model exists and calls it a "step change" in AI capabilities. It is not publicly available.
Anthropic's most powerful AI model ever built leaked by accident on March 26–27, 2026. Claude Mythos (codename: Capybara) sits above the Opus series and dramatically outperforms Opus 4.6 in cybersecurity, coding, and reasoning. It poses unprecedented security risks — good enough to exploit vulnerabilities faster than defenders can respond. Access is restricted to a handful of cybersecurity defense customers. No public API, no pricing, no release date. Meanwhile, Happycapy runs Claude today — with memory, 150+ skills, and Mac Bridge — for $17/month.
How the Leak Happened
On March 26, 2026, cybersecurity researchers Alexandre Pauwels (University of Cambridge) and Roy Paz (LayerX Security) discovered that Anthropic's website was serving a publicly searchable, unencrypted data cache containing thousands of unpublished assets. The misconfiguration was a content management system error, not a deliberate publication.
Fortune magazine broke the story after being tipped off, and an Anthropic spokesperson confirmed the model's existence. CoinDesk followed with updated coverage within hours. The leaked assets included draft blog posts and technical documents describing Claude Mythos's capabilities and deployment strategy.
The Claude Model Tiers — Where Mythos Fits
What Claude Mythos Can Do (According to Leaked Docs)
| Capability | Claude Opus 4.6 | Claude Mythos |
|---|---|---|
| Cybersecurity | Strong — benchmark leader pre-Mythos | "Far ahead of any other AI model" — can identify and exploit vulnerabilities at speed |
| Software coding | Top-tier code generation, refactoring, bug detection | "Dramatically higher scores" across all coding benchmarks |
| Academic reasoning | Excellent mathematical proofs and scientific analysis | "Significantly improved" — mathematical proofs and logical reasoning |
| Agentic workflows | Strong multi-step execution | Enhanced autonomous agents with "more consistent" execution |
| Public availability | Available via API + Happycapy | Not publicly available |
| Pricing | Available on API + Happycapy Pro ($17/mo) | No pricing released |
Why It's Restricted — The Dual-Use Problem
Anthropic's leaked documents don't just celebrate what Claude Mythos can do — they warn about it. The same capabilities that make it extraordinary for cybersecurity defense also make it extraordinarily dangerous in the wrong hands.
The documents specifically warn that a public release of Mythos could enable "a wave of models that will exploit vulnerabilities far faster than defenders can keep up." This is the same reason Anthropic declined the Pentagon's request to use Claude for autonomous weapons — safety constraints are foundational to how the company operates, even when it means delaying or restricting their most capable technology.
High operational costs compound the access problem. Frontier models at this capability level are expensive to run at scale — which is why even the early-access program is limited to a select few customers focused on defense applications.
The Capybara Connection
Claude Mythos is internally codenamed "Capybara" — the world's largest rodent, known for being remarkably calm, social, and cooperative with other animals. In internet culture, capybaras are symbols of chill, boundaryless friendship (they're often photographed relaxing with birds, monkeys, and crocodiles on their backs).
Anthropic chose the name deliberately: even its most powerful model is built around cooperation rather than dominance. The safety-first positioning that led Anthropic to refuse Pentagon contracts, go public benefit corp, and restrict Mythos access — that's the same spirit as the capybara. Powerful. Calm. Not here to hurt anyone.
Happycapy, naturally, is also named after the capybara. The alignment isn't just cosmetic — Happycapy is built on Claude specifically because Anthropic's safety values match what we believe AI assistants should be.
Claude Mythos vs What You Can Actually Use Today
| Feature | Claude Mythos | Happycapy (Claude Sonnet 4.6) |
|---|---|---|
| Public access | No — invite-only early access | Yes — sign up today |
| Price | Unknown (high compute cost expected) | $17/month Pro |
| Persistent memory | Unknown | Yes — MEMORY.md builds over time |
| Skills / tools | Unknown — cybersecurity focus | 150+ skills — research, email, image, video, code |
| Mac Bridge / desktop | Unknown | Yes — full local file + app access |
| Capymail email delivery | No | Yes — async email workflows |
| Agent teams | Unknown | Yes — parallel multi-agent swarms |
| Safety-first company | Yes — Anthropic PBC | Yes — built on Anthropic's Claude |
Claude Mythos is real and it is extraordinary. But it is not for you — not yet, and possibly not ever at a consumer price point. Happycapy runs what Claude is right now: Sonnet 4.6, the best publicly available version, wrapped in the fullest agent infrastructure available to individual users.
Try Happycapy Free — The Best Claude Available to You TodayFrequently Asked Questions
What is Claude Mythos?
Claude Mythos is Anthropic's most powerful AI model to date, positioned above the existing Opus series. It was accidentally revealed on March 26–27, 2026 via a CMS misconfiguration that exposed roughly 3,000 unpublished assets. Its internal codename is "Capybara." It significantly outperforms Claude Opus 4.6 in cybersecurity, software coding, and academic reasoning.
Can I access Claude Mythos?
No. As of March 2026, Claude Mythos has no public API, no pricing, and no public release date. Access is limited to a small group of early-access customers for cybersecurity defense applications. Anthropic cited both unprecedented security risks and high operational costs as reasons for the restricted rollout.
Why is Claude Mythos codenamed "Capybara"?
Anthropic follows a tradition of animal codenames for its models. "Capybara" was the internal name revealed in the leaked documents. The capybara — calm, cooperative, and powerful — reflects Anthropic's safety-first philosophy: even its most capable model is built around cooperation rather than dominance.
What is the best Claude-powered AI assistant available today?
Happycapy runs Claude Sonnet 4.6 with persistent memory, 150+ skills, Capymail, and Mac Bridge — the most fully featured Claude-based platform available to the public. While Claude Mythos remains locked to enterprise security customers, Happycapy gives you the best of what Claude can do today at $17/month.