Anthropic accidentally revealed its next-generation AI model, codenamed “Capybara,” through a CMS misconfiguration. Here’s everything we know about the model that sits above Opus.
How the Leak Happened
On March 26, 2026, Fortune magazine discovered nearly 3,000 unpublished assets — draft blog posts, images, and PDFs — left exposed in a publicly searchable data store linked to Anthropic’s content management system. What those documents revealed shocked the AI world: Anthropic has been quietly testing a new model called Claude Mythos, internally codenamed Capybara, that the company itself describes as “by far the most powerful AI model we’ve ever developed.”
Anthropic confirmed the leak the same day, called it a “human error in CMS configuration,” immediately locked down public access, and — critically — did not deny the model’s existence. Instead, a spokesperson confirmed Mythos is real, currently in early access testing, and represents a “step change” in capability.
Anthropic’s content management system was misconfigured, leaving draft blog posts about Mythos in a publicly searchable data cache. Fortune reviewed the documents before Anthropic locked them down — and the story broke globally on March 27, 2026.
Rather than deny the report, Anthropic leaned into the confirmation. The company acknowledged the model, described its capabilities, and explained its cautious rollout plan. For a company known for its careful, safety-first communications, this was a remarkably candid moment — even if unintentional.
What Is Claude Mythos?
Claude Mythos — codenamed Capybara during internal development — is not an update to an existing model. It is an entirely new tier of AI, sitting above Opus in Anthropic’s lineup.
Anthropic’s own leaked draft put it plainly: “Capybara is a new name for a new tier of model: larger and more intelligent than our Opus models — which were, until now, our most powerful.”
Key confirmed details include:
- New top tier — not a revision of Opus, but a new product category above it
- Early access — currently being trialed by select enterprise customers
- More expensive — described in draft documents as carrying a higher price point than Opus
- Step change — Anthropic’s own language signals this is a generational leap, not an incremental update
Performance: What the Leak Revealed
The leaked draft states that “compared to our previous best model, Claude Opus 4.6, Capybara gets dramatically higher scores” — across software coding, academic reasoning, and cybersecurity.
No exact benchmark numbers have been published yet. But the qualitative framing is notable, especially on cybersecurity. Anthropic’s own safety assessment warns that Mythos is “currently far ahead of any other AI model in cyber capabilities” — a statement framed not as a marketing boast but as a risk disclosure.
To put that baseline in context: Claude Opus 4.6 — the model Mythos outperforms — currently ranks second globally on BrowseComp at 34.44%, behind only Gemini 3 Pro. It’s already a top-tier frontier model. Mythos reportedly clears it by a wide margin.
The Cybersecurity Warning
The most striking detail from the leak isn’t about coding or reasoning — it’s about security risk. Anthropic’s documents suggest Mythos could enable a new class of cyberattacks that outpace existing defenses. In response, the company plans to give cyber defenders access first, to help harden systems before any broader commercial release.
This is a significant departure from typical model launches. It signals that Anthropic views Mythos not just as a product, but as a dual-use capability requiring careful sequencing.
The New Model Tier Structure
Anthropic’s lineup is being rebuilt from the top down. The current public hierarchy runs:
| Tier | Model | Purpose |
|---|---|---|
| ⚡ Speed | Haiku | Fast, cheap, high-volume tasks |
| ⚖️ Balance | Sonnet | Balanced performance and cost |
| 🏆 Power | Opus | Complex reasoning and tasks |
| 🦙 Beyond Opus | Capybara / Mythos | New ceiling — largest, smartest, most expensive |
This is not just a new model — it’s a new pricing tier. Developers building on the Anthropic API should expect Mythos to carry significantly higher costs than Opus, targeted at high-stakes professional and enterprise use cases.
Why This Matters
The Commoditization Counter
The same week this story broke, CNBC was reporting on fears that AI models were becoming commodities — that differentiation between frontier labs was narrowing. Mythos is Anthropic’s direct answer: push the ceiling higher before the competition catches up.
The Enterprise Play
Cybersecurity capability at this level signals a deliberate positioning toward the enterprise market — the highest-value, highest-stakes segment in AI deployment. Companies spending millions defending infrastructure will pay a premium for a model that leads on offense-aware reasoning.
The Competitive Context
OpenAI has GPT-5. Google has Gemini 3 Pro, currently ranked first on BrowseComp. Both are pushing hard at the top of the capability ladder. Mythos positions Anthropic to compete — and potentially lead — at the very frontier. The leak may have been embarrassing, but the timing was nearly perfect: every major AI outlet is now talking about Anthropic.
What We Still Don’t Know
Despite the confirmation, significant details remain unannounced:
- Release date — no official timeline, only “currently in testing”
- Exact benchmark scores — all performance descriptions remain qualitative
- Pricing — described as “more expensive than Opus” with no specific figures
- Context window — not disclosed in any leaked documents
- Multimodal capabilities — unknown whether Mythos extends vision or audio beyond Opus 4.6
- Official announcement — expected to be accelerated now that the cat is out of the bag
Verdict
Claude Mythos is real, confirmed, and coming. It’s the most capable model Anthropic has ever built, it’s already in the hands of early access customers, and the accidental leak almost certainly means the official launch is imminent.
For developers, it’s time to plan for a new top-tier API option with a new pricing tier to match. For enterprises — particularly those in cybersecurity — this may be the most relevant model release of 2026. And for the broader AI market, the message is clear: this is not a plateau.
Watch Anthropic’s blog and announcements closely. The official reveal can’t be far away.
Sources: Fortune (March 26, 2026), Anthropic spokesperson statement, India Today, Firstpost, KuCoin News — March 26–27, 2026.