Claude Fable 5.1

Sep
02
Claude Fable 5.1 banner showing cache reads falling from $1 to $0.25 per million tokens and three breaking changes involving forced tool use, thinking blocks, and edited context.

Claude Fable 5.1 makes caching cheaper and breaks three API behaviors

Cache reads now cost $0.25 per million tokens, but forced tool use and preserved thinking require code changes before some agent workloads can migrate.
4 min read