Anthropic opens Claude Fable 5 to public, limits Mythos 5

Anthropic released Claude Fable 5 to the public on June 9, 2026. The model is included on Pro, Max, Team and Enterprise plans through June 22, 2026; from June 23 users may need usage credits until capacity expands.

Anthropic priced Fable 5 at $10 per million input tokens and $50 per million output tokens, which the company described as less than half the cost of the earlier Mythos Preview. Anthropic will automatically route sensitive queries in cybersecurity, biology, chemistry and model-distillation to Claude Opus 4.8 for further review; those safeguards activate in fewer than 5% of sessions.

Claude Fable 5 is presented as a Mythos-class model with stronger safety guardrails. Claude Mythos 5 uses the same core model with fewer restrictions but remains limited to approved researchers and partners in Project Glasswing, including AWS, Microsoft, Apple and CrowdStrike.

Access to Mythos 5 is restricted to selected biology research teams and Project Glasswing partners. Business customers of Mythos-class models will be subject to a 30-day data retention policy to support safety monitoring.

Anthropic reported performance gains across coding, reasoning, vision, scientific research and long-context tasks. The company said Stripe used Fable 5 to complete a large Ruby codebase migration that would have taken a team more than two months and that the model compressed months of engineering work into days.

Anthropic indicated Mythos 5 delivered roughly 10× speedups in parts of the drug-design process, produced novel scientific hypotheses preferred by researchers about 80% of the time, and ran a week-long autonomous genomics research task that outperformed a recent published model while being about 100× smaller.

Earlier restricted tests of the Mythos Preview demonstrated automated offensive security capabilities. For the public Fable 5 release Anthropic added guardrails and an automatic fallback to Opus 4.8 for queries it classifies as sensitive; the fallback is intended to reduce risk while preserving general-purpose use.

An analyst at Bull Theory noted public pricing for Fable 5 is roughly twice the cost of Anthropic’s most advanced Opus tiers, while earlier Mythos Preview pricing had been about five times Opus levels. Anthropic has reported raising substantial capital and filed confidential paperwork related to an initial public offering.

Anthropic split broader public access through Fable 5 from tightly controlled research access to Mythos 5 and is relying on automatic safety routing and data-retention policies to monitor sensitive activity.