Anthropic Debuts Claude Fable 5 Amid Tightened Security Controls

The company’s decision to release Fable 5 follows months of internal deliberation regarding the risks of the Mythos class. Previously, Anthropic withheld these models, citing potential misuse in high-stakes technical fields. To navigate these concerns, Fable 5 incorporates a fallback mechanism that reverts to the Claude Opus 4.8 model when the system detects high-risk queries. Internal testing shows this system remains active for 95 percent of user sessions.

Alongside the public release, Anthropic is offering Claude Mythos 5, a version with fewer restrictions, currently limited to participants in the private Project Glasswing initiative. Despite the naming convention, the company provided no context for the "5" designation, given the absence of prior Mythos or Fable versions. The pricing structure reflects the model's premium positioning: at $10 per million input tokens and $50 per million output tokens, the cost is double that of the previous flagship, Opus 4.8.