Anthropic released Claude Sonnet 5.5 on 28 September, the second model in its Claude 5.5 family after Opus 5.5. It is pitched as the faster, lower-cost option for well-scoped everyday work (fixing bugs and producing documents, slides and spreadsheets), while Opus 5.5 remains the model for complex, open-ended jobs. It is available on Anthropic’s own platform and through Amazon Web Services, Google Cloud and Microsoft Azure.
Prices are unchanged from Sonnet 5, at $2 per million input tokens and $10 per million output tokens. Anthropic says the new model needs fewer tokens to do the same work, so it costs up to 30% less per task, and that it generates output more than 30% faster.
The largest reported jump is on Terminal-Bench 4.0, an agentic coding test: 70.6%, against 10.3% for Sonnet 5. On several other evaluations it lands within a few points of Opus 5.5. These are Anthropic’s own figures, and the company itself says Opus 5.5 is still clearly stronger at work that needs sustained judgement.
It is also the first Sonnet model to ship with the cybersecurity safeguards Anthropic uses on its most capable models: higher-risk security requests fall back to Sonnet 5, while routine bug-fixing is unaffected.