Large language model
Claude Sonnet 5.5
Claude Sonnet 5.5 is a large language model released by Anthropic on 28 September 2026 as the second model in the Claude 5.5 family. It sits below Claude Opus 5.5 on price, has a 1 million token context window and targets well-scoped everyday tasks, coding fixes, and documents, slides and spreadsheets.
Last reviewed 28 Oct 2026 · by Anthropic
Facts at a glance
| Developer | Anthropic |
|---|---|
| Released | 28 September 2026 source |
| API name | claude-sonnet-5-5 source |
| Context window | 1,000,000 tokens source |
| Max output | 128,000 tokens source |
| Knowledge cutoff | June 2026 (reliable knowledge and training data) source |
| API price | $2 per 1M input tokens, $10 per 1M output tokens, $0.10 cache reads, $2.50 cache writes source |
| Retirement | Not sooner than 28 September 2027 source |
What Claude Sonnet 5.5 is used for
Anthropic describes Sonnet 5.5 as a faster, lower-cost complement to Claude Opus 5.5. It is strongest at well-scoped everyday tasks, fixing bugs and creating documents, slides and spreadsheets. Thinking is adaptive, with medium effort as the default in Claude Code and the Claude apps and high effort on the Claude Platform. Developers who ran Sonnet with thinking off must switch to the new between_tools setting. It is the first Sonnet model to launch with cyber safeguards that fall back to Claude Sonnet 5.
Questions people ask
- When was Claude Sonnet 5.5 released?
- Anthropic announced it and made it available on 28 September 2026.
- How much does Claude Sonnet 5.5 cost?
- $2 per million input tokens and $10 per million output tokens, the same as Sonnet 5, with cache reads cut to $0.10 per million.
- Where is Claude Sonnet 5.5 available?
- On the Claude Platform as claude-sonnet-5-5 and on Amazon Web Services, Google Cloud and Microsoft Azure, according to Anthropic.