Claude Sonnet 5.5: Choosing a Mid-Tier Engine for Daily Agentic Coding
Anthropic shipped Claude Sonnet 5.5 on 2026-09-28: same list price as Sonnet 5, fewer tokens per task, 30%+ faster output, and 70.6% on Terminal-Bench 4.0. A model×harness guide to whether coding-agent defaults should downshift from Opus-class flagships.