Claude Fable 5 API capabilities and pricing

Category: AI
Status: confirmed
Sources: Anthropic announcement, platform docs
Summary: Claude Fable 5 (claude-fable-5) reached general availability on 2026-06-09. It shares the Mythos 5 model weights with always-on adaptive thinking, a 1M-token context window, and 128K output tokens. Pricing is $10 per million input tokens and $50 per million output tokens. Safety classifiers fall back to Opus 4.8 for flagged requests; the API returns stop_reason: "refusal" with classifier details as a 200 response. Available on Claude API, Amazon Bedrock, Vertex AI, and Microsoft Foundry. On subscription plans, Fable 5 is included at no extra cost through 2026-06-22.
Why it matters: Integrations targeting Mythos-class capability should set model to claude-fable-5 and add refusal handling; unhandled refusals will surface as unexpected 200s with no content.