Claude Sonnet 4

#1 for reasoning · Claude Opus 5.5 reads text, images and files, keeps about 1,000 pages in mind at once, and replies up to about 128 pages, with an effort setting as the main dial between depth and speed. Give it edits that span a large codebase, bug hunts, financial or scientific analysis, and charts, diagrams or screenshots full of detail. It needs fewer steps and less output than Opus 5 for the same job and reports back in plainer language. For harder reasoning, Anthropic points to Fable 5.1; for lighter work, Sonnet 5.5.

Haiku 5.5 is the quick, small Claude for high-volume work: summarising, sorting, pulling out details, routing, driving a web browser and acting as a helper agent. It reads text, images and files, keeps about 1,000 pages in mind, replies up to about 128 pages, and has an effort setting while deciding for itself how long to think. It succeeds Haiku 4.5, with better coding and computer use.

#2 for interface design · Claude Sonnet 5.5 reads text, images and files, keeps about 1,000 pages in mind at once, and replies up to about 128 pages, with thinking always on and an effort setting as the main dial. It is Anthropic's pick for well-defined daily jobs: shipping a feature, fixing a bug, or turning notes into finished reports, slide decks and spreadsheets. Lower effort keeps it responsive in agents that work step by step. For high-volume sorting and extraction, Haiku 5.5 is faster; for long, hard projects, Opus 5.5.

#8 for games · Claude Sonnet 5 reads text, images and files, keeps about 1,000 pages in mind at once, and replies up to about 128 pages. It decides for itself how long to think, and you set the effort from low to extra high. Use it for coding, agents that work through a task on their own, and professional work such as documents and analysis; it stops some dangerous requests as they happen.