Anthropic launches Claude Fable 5, first public Mythos-class AI model
The release comes ahead of the company’s anticipated 2026 IPO, with pricing set at double that of its previous flagship Opus 4.8.
Anthropic has released Claude Fable 5, marking the first public launch of its Mythos-class AI model family. The release follows previous statements that the Mythos class was too dangerous for public distribution due to capabilities in cybersecurity and biology. New safety safeguards have been implemented, causing the model to defer to Claude Opus 4.8 in high-risk domains. Anthropic also announced Claude Mythos 5, an unrestricted version of the same underlying model, currently accessible only to select organisations via the Project Glasswing initiative.
Claude Fable 5 is described as the most powerful model Anthropic has made widely available, showing exceptional performance in software engineering, knowledge work, and vision tasks. The model’s lead over competitors reportedly grows as tasks become longer and more complex. In testing, 95 percent of Fable 5 sessions ran entirely on Fable responses without falling back to Opus 4.8.
The model defaults to Claude Opus 4.8 in high-risk areas such as biology and cybersecurity. Anthropic singled out these two domains as areas where the safeguards may block responses, both widely considered sensitive topics for advanced AI systems. The deferral mechanism is intended to mitigate risks associated with the model’s advanced capabilities, which Anthropic has previously described as too capable for unrestricted public distribution.
Pricing for both Fable 5 and Mythos 5 is set at $10 per million input tokens and $50 per million output tokens, which is double the rate of Claude Opus 4.8 but half the cost of Mythos Preview. Access to Claude Mythos 5 is currently limited to users in the Project Glasswing private initiative, with plans to expand access through a "systematic trusted-access program."
This release occurs ahead of Anthropic’s anticipated 2026 IPO. The company did not respond on the record to questions explaining 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 specific technical details of how the new safeguards function beyond blocking responses in specific areas are not fully detailed.
