Anthropic has officially launched Claude Fable 5, the first public version of its controversial “Mythos” AI model. The model recently drew scrutiny after cybercriminals gained unauthorized access prior to its official release. Because Mythos was engineered specifically to identify critical security vulnerabilities, its capabilities present significant risks if misused.

To address safety concerns, Anthropic has implemented strict guardrails for the public rollout. The company conducted over 1,000 hours of testing alongside internal experts and partners to develop advanced safety classifiers. Consequently, any user queries related to cybersecurity, chemistry, biology, or model distillation will automatically be downgraded to the more secure Claude Opus 4.8.

Furthermore, Anthropic is enforcing a mandatory 30-day data retention policy for all traffic, temporarily overriding standard zero-retention agreements even for enterprise clients. This data will be monitored exclusively to detect unauthorized activity and prevent future safety incidents; Anthropic confirms none of this information will be utilized for model training.

The model is currently available to Pro, Max, Team, and Enterprise subscribers until July 22. After this date, usage will transition to a credit-based system, though Anthropic intends to reintegrate the model into subscription tiers in the future. In terms of pricing, Fable 5 and Mythos 5 cost $10 per million input tokens and $50 per million output tokens—double the rate of Opus 4.8.

Despite the high cost and safety restrictions, early enterprise feedback highlights substantial performance gains. According to Workspace and Genspark, the new models outperform all competitors in interface design and game coding. Additionally, analytics firm Hex reported that Fable 5 is the first model to maintain a 90% autonomous execution rate on complex, long-duration analytical tasks without external assistance. Anthropic claims that Fable 5 successfully processes 95% of user requests independently without needing to fall back on Opus 4.8.

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