Which Claude model should I use: Fable 5, Opus, Sonnet, or Haiku?

Claude's lineup is a ladder of capability versus speed and cost, and matching the model to the task is the whole skill. Sonnet 4.6 is the workhorse and the right default for most work: fast, highly capable at writing, analysis, and everyday coding, and excellent value, scoring within a couple of points of the top model on coding benchmarks.

Opus 4.8 sits above it for the hardest jobs: complex reasoning, difficult coding, and high-stakes documents where the extra quality is worth slower, pricier generation. Above even Opus is Fable 5, Anthropic's Mythos-class model, built for the very hardest long-horizon and agentic tasks, where it opens its widest lead. Haiku 4.5 sits at the bottom for speed: quick, cheap, and fine for simple lookups, classification, and high-volume light tasks.

The practical rule is to default to Sonnet 4.6 and escalate deliberately: reach for Opus when a task is genuinely hard and Sonnet is struggling, and reach for Fable 5 for the biggest, most multi-step engineering and reasoning jobs. Using the top model for a simple email just costs more and runs slower for the same result.

For the specifics of the frontier model, see our Claude Fable 5 guide, and for coding specifically, Sonnet and Opus cover the vast majority of needs.