Base model
Same as Fable 5.1
Anthropic differentiates the pair through safeguard and access profiles, not a public fast-versus-smart tier.
Anthropic trusted-access record · checked September 2, 2026
Answer first
Mythos 5.1 is a vetted access profile, not a public upgrade.
It shares Fable 5.1's underlying model but uses different safeguards for approved cyber and life-sciences work. Program eligibility, provisioning, endpoint, data terms, price, and human oversight are part of the model contract.
Verified provider facts
Access
Trusted programs
No consumer upgrade or public self-serve API path is documented in the September 1 launch.
Cyber path
CVP
The Cyber Verification Program will include Mythos-class access for vetted defensive-security work.
Life-sciences path
LSVP
Initial participants are enrolled; broader professional access is planned but must not be assumed.
Choose the access route before the model
General users and developers
Use Fable 5.1 or another generally available model. A public Fable ID, paid plan, or cloud account does not unlock Mythos.
Vetted cyber defenders
Use the Cyber Verification Program route and wait for explicit Mythos-class approval, provisioning, program scope, and endpoint instructions.
Life-sciences professionals
Use the Life Sciences Verification Program route. Anthropic says its safeguards support professional R&D while other safeguards remain in place.
Current US and international applicants
Anthropic says access is currently limited to a set of US organizations while it coordinates broader domestic and international expansion. Verify current enrollment evidence.
Claude Security uses Mythos 5.1 to scan codebases and suggest patches for human review. That is a product-surface fact, not a separate entitlement to the raw model. Compare with the generally available Fable 5.1 record and the 5-to-5.1 safeguard guide.
Governance evidence
- Approved organization, user, domain, and program purpose.
- Exact endpoint, model identifier, region, quota, and contract.
- Acceptable use, safeguards, logging, human review, and incident response.
- Data classification, retention, storage, access, monitoring, and deletion.
- Representative evaluation, denial tests, revocation, and rollback.
Claims this page does not make
- No public Mythos 5.1 API ID or price is asserted.
- Fable 5.1 availability does not create Mythos access.
- "More permissive" does not mean unrestricted or unmonitored.
- EFS transition ZDR is not silently extended to Mythos.
- Anthropic approval does not establish Flowith availability.
Official sources
Fable 5.1 and Mythos 5.1 launch
Shared model, safeguard differences, verified programs, current US access, planned expansion, Claude Security, and public Fable boundaries.
Enterprise Frontier Safeguards
EFS architecture and the exact Fable transition statement used to avoid extending unsupported data claims to Mythos.
Continue by decision
Mythos 5 history
Preserve the previous ID, program history, specs, and migration boundary.
EFS readiness
Check storage, keys, monitoring, reviewers, cost, tests, and rollback without assuming coverage.
Fable 5.1 access
Use the current generally available model when trusted access is unavailable or unnecessary.
Claude Mythos 5.1 questions
Claude Mythos 5.1 is Anthropic's current trusted-access profile of the same underlying model used by Fable 5.1. It uses different safeguards for vetted cybersecurity and life-sciences professionals.
No. Anthropic limits it to trusted access programs. Cyber applicants use the Cyber Verification Program and life-sciences applicants use the Life Sciences Verification Program, with approval and provisioning required.
The September 1 public launch does not document a self-serve first-party API ID for general use. Approved participants should use the exact endpoint and identifier supplied by the trusted program rather than guessing from Fable 5.1 or Mythos 5.
This page does not assert a public Mythos 5.1 contract price. Fable 5.1's public token and cache prices do not prove Mythos pricing, program terms, cloud charges, or entitlement.
Do not assume so from the public launch. Anthropic's EFS transition statement specifically names eligible Fable 5 and Fable 5.1 customers. A Mythos 5.1 participant must verify the exact program, retention, storage, monitoring, and review contract.
This page does not claim a Flowith mapping. Trusted Anthropic access, a cloud relationship, and Claude Security are separate from Flowith's live model catalog, plan, routing, limits, pricing, and data handling.