Anthropic launched Claude Fable 5 on June 9, 2026, as its first widely available Mythos-class model with $10 per million input and $50 per million output token pricing, later updating to Fable 5.1 on September 1 at the same rates alongside improved safeguards and research capabilities. This premium output price has held steady despite the model's strong benchmarks in long-horizon coding and knowledge work. The September 22 release of the smaller Opus 5.5 at $4/$20 pricing, which matches or exceeds Fable 5.1 on several agentic and coding tasks, has intensified competitive pressure on Anthropic's frontier tier. Traders are watching for any 5.2+ announcement that could adjust output rates amid ongoing platform rollouts on AWS, Google Cloud, and Microsoft Foundry, plus potential efficiency gains from cache optimizations seen in recent Opus updates.