Introducing Mythos 5 (Claude Mythos)
Mythos 5 is the most powerful AI model Anthropic has ever built. Codenamed Capybara, Claude Mythos represents a step change in reasoning, coding, and cybersecurity — a new tier above Opus.
What Is Mythos 5?
Mythos 5, officially named Claude Mythos, is Anthropic's next-generation AI model — by far the most powerful the company has ever developed. First revealed on March 26, 2026, through an accidental data exposure reported by Fortune, Mythos 5 introduces a wholly new performance tier, internally designated Capybara, that sits above the existing Opus, Sonnet, and Haiku tiers in the Claude model family. Anthropic confirmed the model's existence and described it as a "step change" in capabilities — the most capable model they have built to date.
The name "Mythos" reflects what Anthropic describes as "the deep connective tissue that links together knowledge and ideas" — signaling a model designed not merely for isolated tasks but for synthesizing complex, multi-domain reasoning at an unprecedented level. The community widely refers to the model as Mythos 5 or Claude Mythos 5, positioning it as the next generational leap beyond the Claude 4.x series. While Anthropic has not officially assigned a version number, "Mythos 5" has become the de facto identifier across developer forums, social media, and prediction markets.
Training for Mythos 5 has been completed. The model is currently in early access testing with a small group of selected customers — with priority given to cybersecurity defense organizations — via the Claude API. Anthropic has emphasized that Mythos 5 is computationally intensive and expensive to run, and is taking a cautious, phased approach to broader availability.
Mythos 5 Core Capabilities
Mythos 5 achieves dramatically higher scores than Claude Opus 4.6 across multiple benchmark categories. Three domains stand out as defining breakthroughs for Claude Mythos.
Software Coding
Enhanced code generation, comprehension, and refactoring capabilities. Mythos 5 performs at the level of a senior engineering team, handling architecture-level tasks with precision.
🧠Academic Reasoning
Markedly improved performance on examination-style questions, theoretical analysis, and multi-step reasoning chains. A generational leap in analytical depth and reliability.
🛡Cybersecurity
Currently far ahead of any other AI model in cybersecurity capabilities. Able to rapidly discover vulnerabilities in codebases, enabling both powerful defense and raising unprecedented risk questions.
Mythos 5: A New Tier in the Claude Family
Mythos 5 is not an incremental update to Opus. Claude Mythos establishes an entirely new tier — Capybara — that extends Anthropic's model lineup to four levels. This represents the first expansion of the Claude tier structure since its original three-tier design.
| Tier | Model | Positioning |
|---|---|---|
| Capybara (New) | Mythos 5 (Claude Mythos) | Most powerful — above Opus, highest cost |
| Opus | Claude Opus 4.6 | Previous flagship, advanced reasoning |
| Sonnet | Claude Sonnet 4.6 | Balanced performance and cost |
| Haiku | Claude Haiku 4.5 | Fastest and most affordable |
Mythos 5 Cybersecurity: The Dual-Use Challenge
In an unprecedented move, Anthropic itself issued a safety warning about Mythos 5's cybersecurity capabilities. Leaked draft materials state that Claude Mythos "presages an upcoming wave of models that can exploit vulnerabilities in ways that far outpace the efforts of defenders."
"In preparing to release Claude Capybara, we want to be extra cautious about understanding the risks it poses — even beyond what our own testing can uncover. We especially want to understand the potential near-term risks in cybersecurity and share those results to help cyber defenders prepare." — From Anthropic's leaked draft blog post, March 2026
This dual-use nature — simultaneously the most powerful AI tool for defense and a potential catalyst for offense — has prompted Anthropic to prioritize early access for cybersecurity defense organizations, giving them time to harden their own codebases before broader release.
The disclosure triggered a significant market reaction: cybersecurity stocks including CrowdStrike and Palo Alto Networks saw sharp declines, with some reports estimating over $14.5 billion in combined market value lost in the week following the leak.
Mythos 5 Release Status and Access
As of March 29, 2026, Mythos 5 (Claude Mythos) is not publicly available. Here is what is confirmed about its current status:
- Training: Completed, along with extensive safety and capability evaluations.
- Early access: Currently being tested with a small group of early access customers via the Claude API, with cybersecurity applications as a priority.
- Expansion: Anthropic states it is "slowly expanding access over the coming weeks," with more information expected in April 2026.
- Cost: Described as "very expensive" for both Anthropic and customers. Efficiency optimization is ongoing before wider rollout.
- Public API: No pricing, SLA, rate limits, or general availability date have been announced.
Concurrently, Bloomberg and The Information reported that Anthropic is considering an IPO as early as Q4 2026, with Mythos 5 positioned as a key capability milestone.
Mythos 5 Industry Impact
Market Reaction
The iShares Technology Software ETF (IGV) dropped nearly 3% on the day of disclosure. Palo Alto Networks (PANW) fell 9.8% in the following week, year-to-date down 18.0%. Investors are reassessing whether AI-native security tools will erode traditional cybersecurity moats.
MCP Ecosystem Growth
Anthropic's Model Context Protocol (MCP) reached 97 million monthly SDK downloads in March 2026, up from approximately 2 million at launch in November 2025 — a 4,750% increase. The ecosystem now includes over 5,800 community and enterprise servers.
Competitive Landscape
Mythos 5 enters a market where Gemini 3.1 Pro and GPT-5.2-Codex compete at the frontier. Opus 4.6 already ranked #1 on Terminal-Bench 2.0 at 65.4%, and Claude Mythos is reported to exceed it substantially across all measured dimensions.
Mythos 5 Performance Benchmarks
While Anthropic has not published a formal system card or benchmark scores for Mythos 5, the leaked drafts assert "dramatically higher scores" across all tested categories compared to Opus 4.6. Below are the current known baselines for Claude Mythos context.
| Benchmark | Opus 4.6 | Sonnet 4.6 | Gemini 3.1 Pro | Mythos |
|---|---|---|---|---|
| SWE-bench Verified | 80.8% | 79.6% | 80.6% | TBA |
| Terminal-Bench 2.0 | 65.4% | 59.1% | 68.5% | TBA |
| ARC-AGI-2 (Verified) | 68.8% | 58.3% | 77.1% | TBA |
| OSWorld-Verified | 72.7% | 72.5% | — | TBA |
| HLE (Partial) | — | 49.0% | — | TBA |
Sources: Anthropic Sonnet 4.6 System Card, Google Gemini 3.1 Pro Model Card. Mythos 5 scores not yet publicly available.
Mythos 5 Frequently Asked Questions
What is the difference between Claude Mythos and Mythos 5?
"Claude Mythos" is the name confirmed through Anthropic's leaked draft materials and media statements. "Mythos 5" or "Claude Mythos 5" is the community designation, reflecting the model's position as the next generational leap beyond the Claude 4.x series. Both names refer to the same model — Anthropic has not officially assigned a version number.
Is Mythos 5 the same as Capybara?
Yes. Capybara is the internal codename and new tier designation for Mythos 5. Claude Mythos is the external product name. Both refer to the same underlying model — Anthropic's most powerful AI system to date.
Can I use Mythos 5 today?
Not yet for general use. Mythos 5 (Claude Mythos) is currently in early access testing with a limited number of selected customers. Anthropic is prioritizing cybersecurity defense organizations and plans to slowly expand access over the coming weeks.