Claude Sonnet 5.5 is Anthropic's September 28th, 2026 Sonnet refresh — Opus-adjacent everyday help at $2/$10. Our tests score helpfulness 93.5, instruction following 95.0, and comprehension 95.5, well above Claude Sonnet 5's 87.5/88.0/89.0. Empathy is 90.5: warmer than Sonnet 4.6's 88.0, short of Opus 5.5's 95.5. Creative writing is 91.5: clearer and more literary than Sonnet 5's 87.0. Speed is 90.0. The default 5.5-family driver when you want strong follow-through without Opus 5.5's bill.