· reAPI Team
Claude Mythos 5.1: What It Is, Who Can Use It and the Price
Claude Mythos 5.1 is the same model as Fable 5.1, offered only to verified organizations. Access rules, $10/$50 pricing, the Cyber Verification Program.
Claude Mythos 5.1 is Anthropic's restricted-access version of Claude Fable 5.1. Anthropic's documentation describes it as "the same model as Claude Fable 5.1, available only to organizations verified through Anthropic's verification programs", with the same specifications and pricing: a 1M-token context, 128K output tokens, and $10 per million input tokens and $50 per million output tokens.[1] It was released on September 1, 2026.[1]
So the question with Claude Mythos is less about what the model can do and more about who may call it and under which rules. This guide covers access, pricing, how it relates to Anthropic's Cyber Verification Program, and what to use if you do not qualify, based on Anthropic's documentation checked on November 4, 2026.
What Mythos 5.1 is
| Claude Mythos 5.1 | Claude Fable 5.1 | |
|---|---|---|
| Model ID | claude-mythos-5-1 | claude-fable-5-1 |
| Availability | Verified organizations only | Generally available |
| Context window | 1M tokens | 1M tokens |
| Max output | 128K tokens | 128K tokens |
| Price per 1M tokens | $10 input / $50 output | $10 input / $50 output |
| Thinking | Adaptive, always on | Adaptive, always on |
| Default effort | high | high |
| Knowledge cutoff | June 2026 | June 2026 |
Source: Anthropic's Claude Mythos 5.1 model page.[1] It is listed on the Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry, each under its own model ID.[1]
The family has earlier members too. Anthropic's pricing page lists Claude Mythos 5 with limited availability at the same base price, and refers to a Claude Mythos Preview.[2] Anthropic publishes a migration guide from Mythos 5 to Mythos 5.1.[1]
Who can use Claude Mythos
Access requires verification. Anthropic says Mythos 5.1 is available only to organizations verified through its verification programs, such as the Cyber Verification Program, and that you request access by applying to the program that covers your use case.[1]
The Cyber Verification Program, updated in October 2026, "makes advanced cyber capabilities and reduced blocking classifiers available to qualifying security professionals". It now has three access tiers covering Claude Opus 5.5, Claude Sonnet 5.5, Claude Mythos 5.1 and new models.[3] Anthropic explains why it exists: its generally available models can be used for secure code review, threat modeling, patching known issues, finding vulnerabilities in your own code and triaging alerts, but "other cyber security work like malware analysis or exploit validation may be interrupted by our safety classifiers".[3]
How to apply, according to the program page:[3]
- Apply through Anthropic's Verification Portal, once per organization; admins assign seats to users.
- Independent researchers, maintainers and bug bounty hunters apply as individuals, but only the Defense tier is open to individuals.
- You need organization and applicant details, a description of your security work and an attestation to the security controls for the tier you want.
- Anthropic aims to reply within seven business days.
- First-party access covers Claude.ai, Claude Code and the Anthropic API; cloud platforms have their own linking steps.
Mythos or Opus 5.5 for security work
Verification does not only unlock Mythos. The same program covers Claude Opus 5.5, which Anthropic calls "our most capable cyber model yet", and Claude Sonnet 5.5.[3] Opus 5.5 lists at $4 and $20 per million tokens against Mythos 5.1's $10 and $50.[1] A verified security team should test both on its own tasks before defaulting to the more expensive model.
Claude Mythos pricing
| Item | Price |
|---|---|
| Input | $10 per 1M tokens |
| Output | $50 per 1M tokens |
| 5-minute cache write | $12.50 per 1M tokens |
| 1-hour cache write | $20 per 1M tokens |
| Cache read | $0.25 per 1M tokens |
| Batch API | 50% off input and output |
Source: Anthropic.[1] The cache read rate is notable: Anthropic prices cache hits on Fable 5.1 and Mythos 5.1 at 2.5% of the base input price, against 10% on most other models.[2] For agents that resend a long context on every turn, that difference outweighs the headline rate.
Two more pricing details from Anthropic affect the real bill. Claude 4.7 and later models use a newer tokenizer that "produces approximately 30% more tokens for the same text", so the same document costs more tokens than it did on older Claude models. And Claude 4.6 and later models include the full 1M-token context at standard pricing: a 900,000-token request is billed at the same per-token rate as a 9,000-token one.[2]
A request with 20,000 input tokens and 2,000 output tokens costs 0.02 × $10 + 0.002 × $50 = $0.30 uncached. If 18,000 of those input tokens are cache reads, it drops to 0.002 × $10 + 0.018 × $0.25 + 0.002 × $50 = $0.1245. These are list-price arithmetic, not measured bills, and they ignore the cost of the first cache write.
If you do not qualify
Most teams do not need Mythos at all. Anthropic's own description is that it is the same model as Fable 5.1, which anyone can use, and that general-availability models already cover secure code review, threat modeling and finding bugs in your own code.[1][3] Where verification matters is security work that the standard safety classifiers may interrupt, such as malware analysis or exploit validation, which is the case Anthropic's program describes.
If your work is ordinary engineering, writing or analysis, use Claude Fable 5.1, or a cheaper tier: Anthropic lists Opus 5.5 at $4 and $20, and Sonnet 5.5 at $2 and $10.[1]
FAQ
Is Claude Mythos better than Claude Fable 5.1?
Anthropic describes Mythos 5.1 as the same model as Fable 5.1, with the same specifications and pricing; access is what differs.[1]
How do I get access to Claude Mythos?
Apply through one of Anthropic's verification programs, such as the Cyber Verification Program, via its Verification Portal.[1][3]
Is Mythos 5.1 available on Amazon Bedrock?
Anthropic lists a Bedrock model ID, anthropic.claude-mythos-5-1. Its Cyber Verification Program page says Bedrock access is available only to customers with Enterprise Frontier Safeguards.[1][3]
Using Claude Fable 5.1 instead of Claude Mythos
For everyone outside the verification programs, Claude Fable 5.1 is the route to the same model. reAPI serves Claude Fable 5.1 at $7 per million input tokens and $35 per million output tokens, as shown on its model page on November 4, 2026, with no verification step. Claude Mythos remains the option for verified security teams whose work the standard classifiers block.
References
- Anthropic. Claude Mythos 5.1 model overview. Retrieved November 4, 2026 from platform.claude.com/docs/en/models/mythos-5-1/overview
- Anthropic. Pricing. Retrieved November 4, 2026 from platform.claude.com/docs/en/about-claude/pricing
- Anthropic. Cyber Verification Program. Retrieved November 4, 2026 from support.claude.com/en/articles/14604842