Anthropic's Claude model guide: choosing between Fable, Opus, Sonnet and Haiku

Which Claude model should you build with? Fable, Opus, Sonnet, or Haiku

Anthropic's selection guide says most coding and knowledge work should start with Claude Opus 5.5 at medium thinking effort, moving to Sonnet 5.5, Haiku 5.5 or Fable 5.2 as task difficulty changes. It frames model choice around the cost of finishing a task: set up automated acceptance checks first, then adjust thinking effort or step up a model, and hand easy-to-verify side tasks to smaller models.

Why it matters: Anthropic splits Claude selection into model, thinking effort and cost per finished task, and proposes automated acceptance checks plus reruns on failure to control spend.