Anthropic releases Claude Fable 5, first public Mythos-class model at $10/$50 per million tokens

Anthropic has released Claude Fable 5, the first broadly available model from its Mythos class, which the company previously said was too dangerous to release publicly due to exceptional cybersecurity capabilities.

Pricing and availability

Fable 5 is priced at $10 per million input tokens and $50 per million output tokens — double the rates of Claude Opus 4.8, Anthropic's previous flagship model. The pricing is half what users currently pay for Mythos Preview access.

Safeguards and fallback mechanism

According to Anthropic, the release is "made possible by new safeguards that block responses in specific high-risk areas." When Fable 5 determines a query falls into a restricted category, it falls back to Claude Opus 4.8, which Anthropic described as particularly strong on "honesty" when launched last month.

The company singled out cybersecurity and biology as domains where safeguards may trigger. In testing, 95 percent of Fable sessions ran entirely on Fable responses without requiring fallback to Opus 4.8.

Performance claims

Anthropic claims Fable 5 "shows exceptional performance in software engineering, knowledge work, and vision," with its lead over other models growing as tasks become longer and more complex. The company describes it as "the most powerful model it has ever made widely available."

Claude Mythos 5: Limited access variant

Anthropic is also releasing Claude Mythos 5, which the company says is "the same underlying model as Fable 5, but with the safeguards lifted in some areas." Access to Mythos 5 appears limited to organizations in Anthropic's Project Glasswing initiative, which the company describes as "not entirely watertight." Anthropic said it plans to "expand access over time through a more systematic trusted-access program."

Unanswered questions

Anthropic did not explain how either model relates to Claude Mythos Preview or why the models are numbered "5" when there appear to be no previously released Mythos or Fable models. The company did not respond to requests for comment on these questions.

What this means

This release represents a significant shift in Anthropic's approach to powerful model deployment. Rather than withholding capable models entirely, the company is attempting to balance broad access with safety through automated guardrails and selective fallback to less capable systems. The dual-release strategy — a safeguarded public version and a less-restricted private version — suggests Anthropic is testing how to commercialize highly capable models while managing risks the company itself has identified as serious. The missing context about previous Mythos/Fable versions and the relationship to Mythos Preview raises questions about Anthropic's model versioning and communication strategy.