- Fable 5.1 and Mythos 5.1 are the same underlying model with different safeguard configurations.
- Claude Fable 5.1 is generally available today across Anthropic’s platforms and cloud partners (AWS, Google Cloud, Microsoft Azure) and via the Claude API (claude-fable-5-1).
- Claude Mythos 5.1 is only available through Anthropic’s trusted access programs for vetted cyberdefense and life‑science organisations; availability is currently limited to a set of US organisations while Anthropic coordinates with US government partners to expand access.
- Anthropic described Enterprise Frontier Safeguards (EFS) to let eligible customers store data on their cloud infra and receive zero data retention while enabling customer‑conducted human review by default.
- Claude Mythos 5.1 has more permissive safeguards tailored for cybersecurity and life‑sciences work and is being used to power Anthropic’s Claude Security code‑scanning product.
- EFS rollout will begin in phases starting this fall; customers can request access via Anthropic’s form.
- Developers can access claude-fable-5-1 on the Claude API and through cloud partners listed in the announcement.
- Organisations seeking Mythos 5.1 for cyberdefense are directed to register interest through Anthropic’s CVP process; broader international access is being coordinated with government partners.
- Anthropic highlighted discounted support for scientists and grants through its AI for Science program and a Claude Team plan for researchers.
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