Claude Mythos 5.1
Claude Mythos 5.1 is the invite-only twin of Claude Fable 5.1, released September 1, 2026 through Anthropic's Project Glasswing trusted-access programs for cyberdefenders and life-science researchers.
Provider
Anthropic
Model family
Anthropic Claude
Multimodal LLM
Cost tier
Mythos
Status
Preview
Release Sep 1, 2026
Why teams choose it
Anthropic states Fable 5.1 and Mythos 5.1 are the same model with different safeguards
Mythos is not a separate consumer SKU.
Access is through Cyber Verification and Life Sciences programs
contact Anthropic, AWS, or Google Cloud account teams.
Anthropic reports Mythos 5.1 at 60.9% on Terminal-Bench 4.0 vs 55.8% for Fable 5.1
under production Fable safeguards.
Tradeoffs to know
- Not on Claude Pro, Max, Team, or general Enterprise self-serve plans.
- Biology and cyber permissions remain program-gated even after an invite.
When not to use this
- Current trusted-access rollout is limited; do not catalog it as a drop-in Fable 5.1 replacement.
Benchmarks
- Terminal Bench 4 0 Mythos
- 60.9
Technical specs
- Inputs
- text, image
- Outputs
- text
- License
- Proprietary API (invite only)
- Same Specs As
- claude-fable-5-1
- Capabilities
- defensive cybersecurity
- life-science research
- long-horizon coding
- adaptive thinking
- long context
Anthropic Claude family lineup
Current models
Previous versions
Related models
Claude Mythos 5.1 FAQ
What is Claude Mythos 5.1?
Claude Mythos 5.1 is the invite-only twin of Claude Fable 5.1, released September 1, 2026 through Anthropic's Project Glasswing trusted-access programs for cyberdefenders and life-science researchers. It shares Fable 5.1 specifications and $10/$50 pricing, with more permissive cybersecurity and biology safeguards for vetted organizations.
When does Claude Mythos 5.1 fit best?
Vetted defensive vulnerability research
What should teams watch out for with Claude Mythos 5.1?
Not on Claude Pro, Max, Team, or general Enterprise self-serve plans.
Explore next
Models, tools, and comparisons that connect to this reference.