Anthropic's mid-tier model that lands within a few points of Opus 5.5 at half the price
NewAdded Sep 28, 2026
Claude Sonnet 5.5 is Anthropic's September 28, 2026 update to Sonnet 5 and the second model in the Claude 5.5 family after Opus 5.5. It keeps Sonnet 5's price of $2 per million input tokens and $10 per million output ($0.20 cache reads, $2.50 cache writes), generates output more than 30% faster, and in Anthropic's testing costs up to 30% less per task because it uses fewer tokens and tool calls. Anthropic's own benchmarks put it ahead of Opus 5.5 on Terminal-Bench 4.0 (70.6% vs 66.4%) and within two points of it on OSWorld 2.1 (80.1% vs 81.8%) and GDPval-AA v2.1 (1844 vs 1846). It is the first Sonnet to carry Opus-level cybersecurity safeguards, which route higher-risk security requests back to Sonnet 5.
Why: It is the rare mid-tier release that closes almost the whole gap to the flagship on agentic work while costing half as much per token, and Anthropic's customer reports (Box, Zendesk, Lovable, Base44) all point the same way: fewer steps and fewer tokens for the same result. For most Claude users it is the new default to try before paying for Opus.
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Anthropic released Sonnet 5.5, which it says runs about 30 percent faster and consumes significantly fewer tokens than Sonnet 5, released three months earlier. Despite sitting below the flagship Opus line, Sonnet 5.5 outperforms Opus 5.5 on agentic coding task…