Overview
- Anthropic released Claude Sonnet 5.5 on Monday, Sept. 28, as the second model in its Claude 5.5 family and said a smaller Haiku 5.5 will arrive in coming weeks.
- The company says Sonnet 5.5 generates output more than 30% faster than Sonnet 5 and can lower cost per task by up to 30% because it needs fewer input and output tokens.
- In Anthropic's benchmark results Sonnet 5.5 narrowed the gap with flagship Opus 5.5 on many tests and outperformed Sonnet 5 on coding: Sonnet 5.5 scored 70.6% on Terminal‑Bench 4.0 versus 10.3% for Sonnet 5 and 66.4% for Opus 5.5.
- List token prices for Sonnet remain $2 per million input tokens and $10 per million output tokens, but Anthropic says effective run costs fall; Sonnet 5.5 is available now on the Claude Platform, AWS, Google Cloud, and Microsoft Azure.
- Anthropic extended Opus‑level cybersecurity safeguards and fallbacks to Sonnet 5.5 because of improved cyber capabilities, and it framed the release as part of a product push before an IPO even as vendor‑run benchmarking awaits wider independent verification.