Anthropic announced Claude Sonnet 5.5 on September 28, 2026, the second model in its Claude 5.5 family. The company says it is a clear upgrade over Claude Sonnet 5, running more than 30% faster and costing up to 30% less for most work.
Sonnet 5.5 is positioned as a faster, lower-cost complement to Claude Opus 5.5. While Opus 5.5 targets complex work requiring careful judgment, Sonnet 5.5 focuses on well-scoped everyday tasks, bug fixing, and creating polished documents, slides, and spreadsheets. It is now the model powering the free tier on claude.ai.
Claude Sonnet 5.5 Performance and Specs
Anthropic reports major gains on several benchmarks. The model scores 70.6% on Terminal-Bench 4.0, an agentic coding evaluation, compared to Sonnet 5's 10.3%. It also scores two points below Opus 5.5 on GDPval-AA, which tests real-world work across various occupations.
- Pricing: $2 per million input tokens, $10 per million output tokens, $0.20 per million cache read tokens — same as Sonnet 5
- Cost per task: up to 30% less than Sonnet 5 due to fewer tokens needed
- Speed: generates outputs 30%+ faster than Sonnet 5, the fastest Sonnet model to date
- Terminal-Bench 4.0: 70.6% versus Sonnet 5's 10.3%
- First Sonnet model to beat Pokémon Red working only from screenshots
