Claude Sonnet 5.5 is Anthropic's Sonnet-class model (1M-token context, 128K max output, $2/$10 per million input/output tokens), released September 28, 2026 as a direct upgrade to Sonnet 5 and a faster, lower-cost complement to Opus 5.5. It generates output over 30% faster with fewer tokens per task, and is strongest at well-scoped everyday work such as building features, fixing bugs, and producing polished documents, slides, and spreadsheets.
Claude Haiku 4.5 is Anthropic's fast, affordable small model in the Claude 4 generation, balancing strong instruction-following and coding ability with low latency. It is designed for high-throughput agentic and chat applications where speed and cost efficiency are priorities.