What is Claude Mythos?
Claude Mythos is Anthropic's model class for advanced cybersecurity and biology research, available only to vetted cyber defenders and life scientists through Anthropic's verification programs. The current version, Claude Mythos 5.1, was introduced on September 1, 2026 and starts at $10 per million input tokens and $50 per million output tokens.
What can you do with it?
Anthropic positions Mythos as its most capable model class for cybersecurity and biology research. Claude Mythos 5.1 and Claude Fable 5.1 are the same underlying model: Fable 5.1 adds safeguards for cybersecurity and biology, while Mythos 5.1 is offered without them to vetted organizations. Anthropic says the gap between their benchmark scores reflects tasks where Fable's safeguards intervene.
Typical users are security teams that need deep vulnerability research and life scientists working on dual-use biology. Anthropic's Claude Security product also runs on Mythos 5.1.
Check whether you need it
Suggested workflow: before applying, run your task on Claude Fable 5.1, which anyone can use through the API. Anthropic says Fable 5.1 can now identify software vulnerabilities in source code and that its biology safeguards intervene on benign requests 85% less often than Fable 5's.
If Fable still refuses or falls short on legitimate work, document the cases and apply through the Cyber Verification Program or the Life Sciences Verification Program. The Cyber Verification Program also unlocks advanced cyber capabilities on Claude Opus 5.5 and Claude Sonnet 5.5, which may be enough before applying for Mythos.
Pricing and access
Mythos 5.1 is available only to vetted cyber defenders and life scientists through Anthropic's trusted access programs. Pricing starts at $10 per million input tokens and $50 per million output tokens, the same list price as Fable 5.1. Using it requires accepting a 30-day data retention policy for safety monitoring by default.
Earlier versions show how access has shifted: Mythos 5 was limited to a small group of vetted partners, was briefly unavailable in June 2026, and access for a set of US organizations was restored on July 1 after export controls were lifted.
What stands out
- Same underlying model as Claude Fable 5.1, without its cyber and biology safeguards
- Access through trusted access programs only
- 30-day data retention for safety monitoring by default
- Claude Security runs on Mythos 5.1
Before you choose
- Not available to the general public; approval is required.
- 30-day data retention for safety monitoring by default.
- Fable 5.1 offers the same model with safeguards for most users.
Go to the source
Sources & further reading
Based on the official documentation below. Features and access can change; check the provider before making a decision.
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