Which model is worth using
1 Oct 2026
Anthropic
Claude is split by job. Fable 5.1 is the top of the range. Opus 5.5 is the flagship most people should start with. Sonnet 5.5 is the fast complement. Haiku 4.5 is the older small model.
Claude Opus 5.5
22 Sep 2026 · Closed · Anthropic's current flagship. At max effort it leads the 1 Oct 2026 Intelligence Index at 58. At high effort it is 54, for $1.82 a measured task.
Claude Sonnet 5.5
28 Sep 2026 · Closed · The fast Claude. Two points behind Opus at max effort on the index, and more expensive per measured task because it spends more output tokens.
Claude Fable 5.1
1 Sep 2026 · Closed · Anthropic's top-of-range model for demanding reasoning. On this index it no longer leads. Opus 5.5 and Sonnet 5.5 both passed it after it launched.
Claude Haiku 4.5
Oct 2025 · Closed · Kept on the board so the Claude ladder is honest. Index 17. Useful only when the call is easy and the surrounding stack is already Claude.