Anthropic released Claude Sonnet 5.5 on Sept. 28, the second model in its Claude 5.5 family, available across Claude and its APIs. Anthropic calls it a clear upgrade over Sonnet 5 that runs more than 30% faster and costs up to 30% less for most work, and a lower-cost complement to the flagship Opus 5.5. Claude Haiku 5.5 will join the family in the coming weeks.

Grey tests in Claude Code ahead of the release showed pricing of $2 per million input tokens and $10 per million output tokens, with cache reads at $0.20 per million, half the rates of Opus 5.5. The model identifier claude-sonnet-5-5 appeared in a Claude Code update before the launch.

Opus 5.5, the first model in the family, was released Sept. 22 at $4/$20 per million input/output tokens and ranks No. 2 in Agent Arena and No. 1 on Xbench.