Anthropic’s new Fable release is cheaper, less restrictive

On Tuesday, Anthropic released Fable and Mythos 5.1, twinned versions of the company’s most advanced AI model. In addition to performance upgrades, the new Fable release includes changes meant to reduce token cost and false-positive restrictions from the model’s safeguards.

As with the previous Mythos model, Mythos 5.1 will only be available to registered Anthropic partners engaged in either cybersecurity or life sciences research. Fable 5.1, the unrestricted version, is available starting today on cloud platforms or through the Anthropic API.

One of the most significant changes is Anthropic’s previously reported embrace of Zero Data Retention, allowing clients to run Anthropic models on their own infrastructure without data outflows. Previously unavailable for Fable due to security concerns, a high-privacy service (called Enterprise Frontier Safeguards) will now roll out to users in June. Notably, the system will still monitor for misuse by agents or human users, but clients will control how the monitoring takes place.

As part of the announcement, Anthropic assured customers that their data had not been inappropriately accessed. “Anthropic has never trained on enterprise data without explicit permission, and never will,” the announcement reads.