Claude Mythos 5.1
The same model as Claude Fable 5.1, with safeguards set for vetted cybersecurity and life-sciences teams. Not available to the general public.
- Made by
- Anthropic
- Released
- Type
- Specialist
- Status
- Live
- How to get it
- Only through Anthropic's trusted access programs for cybersecurity and life-sciences work
- Good for
- Security researchLife-sciences research
What it is
Mythos 5.1 and Fable 5.1 are one model released on September 1, 2026, with two levels of safeguards. Fable 5.1 is open to everyone. Mythos 5.1 has its safeguards tuned for professional security and biology work, where the default filters would block legitimate tasks.
Who can use it
Only organisations accepted into Anthropic’s trusted access programs. Teams apply through Anthropic or through their AWS or Google Cloud account team. Specs and prices match Fable 5.1: a 1 million token context window, $10 per million input tokens and $50 per million output tokens.
What it means for you
Unless you work in security research or the life sciences inside an approved organisation, you will use Fable 5.1 instead. Mythos is worth knowing about because it shows where the AI labs are heading: one strong model, with different access levels for different kinds of user.