Claude Fable 5.1 Now on OpenRouter and Vercel AI Gateway

What shipped

Anthropic released Claude Fable 5.1, a new Mythos-class model built for autonomous knowledge work and coding. It went live on OpenRouter and Vercel AI Gateway on September 1, 2026.

What changed

Fable 5.1 improves on Fable 5 across three areas: agentic coding (long code refactors, front-end and visual work), long-running agentic workflows, and knowledge work. It retains the same 1,000,000-token context window and supports text, image, and file inputs with text output, including reasoning, structured outputs, and verbosity controls.

Pricing is unchanged from Fable 5: $10 per million input tokens, $50 per million output tokens. Input cache reads drop to $0.25/M and cache writes are $12.50/M (or $20/M with 1-hour retention).

On Vercel AI Gateway, Fable 5.1 is available with a single API key, automatic fallbacks, spend tracking, and traces. OpenRouter routes it through anthropic/claude-fable-5.1; the ~anthropic/claude-fable-latest alias will redirect to 5.1.

Why a builder cares

Same price as Fable 5 but stronger at agentic coding and long-running tasks — an easy upgrade path through OpenRouter's latest alias or Vercel's gateway. If you were routing agent traffic to Fable 5, you get better results for the same per-token cost starting today.