Claude Mythos FAQ

Claude Mythos is Anthropic's most powerful AI model ever built, internally codenamed Capybara. It represents an entirely new model tier above Claude Opus — not an incremental update, but what Anthropic describes as a "step change" in capabilities. The model demonstrates dramatically higher performance across software coding, academic reasoning, and cybersecurity compared to all previous Claude models.

The name "Mythos" was chosen deliberately. According to Anthropic's leaked draft materials, it refers to "the deep connective tissue that links together knowledge and ideas" — reflecting the model's ability to synthesize understanding across domains in ways that prior models could not. Training has been completed, and the model is currently in limited early access with selected customers and partners.

"Claude Mythos" is the name that appeared in Anthropic's leaked draft blog posts and marketing materials, and was subsequently confirmed by an Anthropic spokesperson. It is the official product name for the model.

"Claude Mythos 5" or simply "Mythos 5" is an unofficial community designation that emerged after the leak. The "5" reflects the model's position as the next generation after the Claude 4.x family (which includes Claude Opus 4.6, Sonnet 4.5, etc.). However, Anthropic has not assigned an official version number to the model. Both names refer to the same underlying system — the Capybara-tier model that sits above Opus in Anthropic's hierarchy. For accuracy, "Claude Mythos" without a version number is the more precise designation based on available information.

Yes. Capybara is Anthropic's internal codename and the new tier designation for the model, while Mythos is the external product name intended for public use. They refer to the same underlying model. Anthropic uses animal-based codenames for its model tiers — Haiku (smallest/fastest), Sonnet (mid-range), Opus (high-end) — and Capybara now occupies the new top tier above Opus. Just as "Opus" is both a tier name and part of a product name (e.g., "Claude Opus 4.6"), Capybara serves as the tier while Mythos serves as the customer-facing brand.

Claude Mythos achieves "dramatically higher scores" than Claude Opus 4.6 across software coding, academic reasoning, and cybersecurity benchmarks. This is not a modest improvement — Anthropic characterizes it as an entirely new tier of capability rather than an incremental update within the existing Opus line.

For context, Claude Opus 4.6 was already a top-performing model, scoring 80.8% on SWE-bench Verified, 68.8% on ARC-AGI-2 Verified, and 72.7% on OSWorld-Verified. Mythos substantially exceeds these figures, though Anthropic has not yet published exact benchmark numbers. The model is also described as much larger, smarter, and more expensive to operate — reflecting the significant computational resources required to deliver this level of performance. For detailed benchmark analysis, see our benchmarks page.

No direct benchmark comparison between Claude Mythos and competing models from OpenAI or Google is available yet, as Mythos has not been submitted to independent third-party evaluation platforms. However, the baseline is informative: Claude Opus 4.6 was already competitive with Google's Gemini 3.1 Pro and surpassed OpenAI's GPT-5.2-Codex on several benchmarks, including SWE-bench Verified and Terminal-Bench 2.0.

Since Anthropic claims that Mythos dramatically exceeds Opus 4.6 across all measured capabilities, it would represent a significant lead over current competitors if those claims hold up under independent testing. Until third-party benchmarks are published, all comparisons remain based on Anthropic's internal evaluations — which, while informative, have not been independently verified.

Anthropic has not officially disclosed the parameter count for Claude Mythos. Community speculation has centered around approximately 10 trillion parameters, but this figure is entirely unverified and should be treated with significant caution. Anthropic has never publicly confirmed parameter counts for any of its Claude models as a matter of policy — this applies to Haiku, Sonnet, and Opus as well.

The only confirmed characterization is that Mythos is "much larger and smarter" than Claude Opus, which itself is the largest model in the current Claude lineup. Parameter count alone is also an imperfect proxy for capability, as architectural innovations, training data quality, and post-training techniques all contribute substantially to model performance.

With the introduction of Claude Mythos, Anthropic's model lineup now has four tiers instead of the previous three. From most to least powerful:

• Capybara (Claude Mythos) — the new top tier, most capable and most expensive
• Opus — previously the top tier, high-end performance for complex tasks
• Sonnet — mid-range, balancing capability with speed and cost
• Haiku — fastest and most affordable, optimized for high-throughput use cases

This four-tier structure gives Anthropic a broader range of offerings for different use cases and budget requirements. For a detailed breakdown, see our model tier page.

As of March 2026, Claude Mythos is in early access with a small group of selected customers and partners. Anthropic has not announced a specific public release date but has stated it is "slowly expanding access over coming weeks." The company is taking a cautious, phased approach to deployment — driven in large part by the model's unprecedented cybersecurity capabilities, which Anthropic wants to ensure are deployed responsibly.

More information about availability, pricing, and rollout plans is expected in April 2026. Anthropic has indicated that cybersecurity defense organizations will receive priority access before general availability. For a complete timeline of events, see our timeline page.

Anthropic has not announced official pricing for Claude Mythos. The model has been described as "very expensive" for both Anthropic to operate and for customers to use. For context, the current Claude Opus tier is priced at $15 per million input tokens and $75 per million output tokens via the API. Given that Mythos represents a substantially larger and more computationally intensive model, pricing is expected to be significantly higher than Opus.

Anthropic has indicated it is actively working to optimize the model's computational efficiency before a wider rollout — suggesting that the current cost structure may be a factor delaying general availability. The eventual pricing will likely reflect both the raw computational cost and the model's positioning as Anthropic's premium offering for the most demanding applications.

No. Any website claiming to offer free access to Claude Mythos 5 is extremely unlikely to be an official Anthropic service. As of March 2026, Claude Mythos is only available through a limited early access program with selected partners. There is no free public access of any kind.

Websites making such claims pose serious risks, including:

• Fake models that merely imitate AI responses using a lesser model or scripted replies
• Phishing for personal information, email addresses, or payment details
• Credential theft targeting your Anthropic, Google, or other service logins
• Malware distribution disguised as "required downloads" or browser extensions

You should only access Claude models through official Anthropic channels: claude.ai, the Anthropic API at api.anthropic.com, or authorized partner platforms like Amazon Bedrock and Google Cloud Vertex AI.

According to Anthropic's own leaked draft materials, Claude Mythos is "currently far ahead of any other AI model" in cybersecurity capabilities. The model can rapidly discover vulnerabilities in codebases — scanning for security flaws with a speed and thoroughness that exceeds manual code review and traditional static analysis tools. It understands not just individual vulnerability patterns but the complex chains of seemingly innocuous code that, when combined, create exploitable attack surfaces.

This makes Mythos both an extraordinarily powerful defense tool — enabling organizations to audit codebases, identify weaknesses before attackers do, and prioritize remediation — and a significant dual-use risk. Anthropic took the unprecedented step of issuing a safety warning about its own model's capabilities and is prioritizing early access for cybersecurity defense organizations to give defenders a head start. For a full analysis, see our cybersecurity page.

Anthropic is applying its Constitutional AI framework to Claude Mythos alongside a defense-first release strategy. The key elements of this approach include:

• Priority access for defense: cybersecurity defense organizations receive early access before general availability, giving defenders a head start
• Phased deployment: a cautious, gradual rollout rather than a broad immediate release, allowing Anthropic to monitor real-world usage and adjust safeguards
• Ongoing internal evaluation: continuous safety testing and red-teaming to identify and mitigate potential risks
• Unprecedented self-warning: Anthropic issued a public safety warning about its own model's capabilities, particularly in cybersecurity

Anthropic has not yet published a system card or model card for Mythos, though these documents are standard practice and are expected to accompany a broader public release. The fact that Mythos triggered internal safety thresholds that previous models did not suggests Anthropic is treating this deployment with an elevated level of caution. For more detail, see our safety page.

On March 26, 2026, a CMS (content management system) configuration error at Anthropic exposed approximately 3,000 unpublished content assets — including draft blog posts, benchmark data, marketing materials, and internal documentation about Claude Mythos — in a publicly searchable data store. The leak was discovered independently by a Fortune journalist and two security researchers.

Anthropic attributed the incident to "human error" in their content management system configuration and moved quickly to remove the exposed materials. However, the data had already been widely copied and archived. The exposed materials included detailed performance benchmarks, the Capybara tier designation, pricing discussions, Anthropic's own safety warnings about the model's cybersecurity capabilities, and draft marketing copy describing Mythos as "the most powerful AI model ever built." For a complete chronology, see our timeline page.

The timing is notable but no direct connection has been confirmed. On March 27, 2026 — the same day that major outlets published coverage of the Claude Mythos leak — Bloomberg and The Information reported that Anthropic was in discussions for an initial public offering targeting Q4 2026.

Positioning Mythos as "the most powerful AI model ever built" could certainly support Anthropic's IPO valuation narrative — demonstrating technical leadership and a differentiated product at the premium end of the market. The convergence of a flagship model announcement and IPO discussions has drawn attention from industry analysts and investors. However, Anthropic has not publicly commented on any connection between the two, and the leak itself was attributed to an unintended configuration error rather than a deliberate disclosure strategy.