Anthropic has released Claude Fable 5, a broadly available Mythos-class model, while keeping Claude Mythos 5 restricted to approved Project Glasswing and trusted-access customers. The company’s pitch is not simply that the model is more capable. It is that the same underlying capability can be made commercially available through a release boundary: classifiers, refusal and fallback behavior, trusted access, and thirty-day safety retention.

Sam Ellis reports on why that boundary is the product. For developers and enterprise buyers, Fable 5 is generally available across Anthropic’s API and major cloud platforms, with a one-million-token context window, up to 128,000 output tokens, and pricing at $10 per million input tokens and $50 per million output tokens. But Fable 5 and Mythos 5 are also designated Covered Models, which means thirty-day data retention and no zero-data-retention option.

The episode follows Anthropic’s launch announcement, model documentation, and system card, then pressure-tests the public/private split against independent coverage from CyberScoop, Reuters via BNN Bloomberg, and The Next Web. The question is whether Anthropic can commercialize restricted capability by making the safeguard legible, durable, and verifiable enough to survive real customers and real adversaries.

Sources

Anthropic: “Introducing Claude Fable 5 and Claude Mythos 5” — primary launch source for Fable 5 as a Mythos-class model made safe for general use, Mythos 5 as the same underlying model with safeguards lifted for approved customers, fallback-rate claims, Project Glasswing access, pricing, and thirty-day safety retention.
Anthropic Claude docs: “Introducing Claude Fable 5 and Claude Mythos 5” — source for API IDs, availability, refusal behavior, fallback configuration, Covered Model status, and retention limits.
Anthropic Claude docs: model overview — source for general model availability, 1M-token context, 128k output limit, cloud-platform availability, and listed pricing.
Anthropic: Claude Fable 5 / Mythos 5 system card — primary safety source for the two-configuration model architecture, cyber and bio risk rationale, CB-1 / CB-2 discussion, safeguard claims, and Anthropic’s warning that some judgments are less clear than for previous models.
Anthropic system-card PDF — direct PDF copy of the system card used for source verification.
CyberScoop: “Anthropic releases Claude Fable 5, a public version of Mythos with guardrails” — independent pressure-test source for the “Mythos on a leash” framing, the absence of universal jailbreaks in testing, and the unresolved question of public adversarial pressure.
Reuters via BNN Bloomberg: “Anthropic rolls out public version of Mythos without cybersecurity capability” — mainstream commercial framing of the public Fable / restricted Mythos split and the student vulnerability-seeking example described by Anthropic.
The Next Web: “Anthropic launches Claude Fable 5, a public version of its cyber-focused Mythos model” — background business context on pricing, paid-subscriber and enterprise access, and the monetization pressure around the release.

Email: SamEllisShow@protonmail.com