Claude Sonnet 5.5 is the Anthropic model that balances speed and intelligence. Anthropic released it on September 28, 2026, and says it runs at least 30 percent faster than Sonnet 5 and costs up to 30 percent less for most work.
Key facts
| Item | Claude Sonnet 5.5 |
|---|---|
| Maker | Anthropic |
| Released | September 28, 2026 |
| API model ID | claude-sonnet-5-5 |
| Context window | 1 million tokens |
| Max output | 128,000 tokens |
| Knowledge cutoff | June 2026 |
| Default effort | high, with adaptive thinking |
| API price per million tokens | $2 input, $10 output, $0.10 cache reads |
Sources: Anthropic's models overview and pricing page, plus the Sonnet 5.5 announcement, checked October 24, 2026.
Pricing details
Sonnet 5.5 costs $2 per million input tokens and $10 per million output tokens. On October 7, 2026, Anthropic halved its cache read price to $0.10 per million tokens. Batch API requests are half price. Fast mode is not offered on Sonnet.
Where to use Claude Sonnet 5.5
- API and clouds: on the Anthropic API, Amazon Bedrock, Claude Platform on AWS, Google Cloud and Microsoft Foundry.
- Claude apps: available on every Claude plan, including Free.
Strengths and limits
On some of Anthropic's own benchmarks Sonnet 5.5 comes close to or beats Opus 5.5, but Anthropic says Opus 5.5 "remains clearly stronger at complex, open ended work requiring sustained judgment." Sonnet suits well scoped tasks, bug fixes, documents and slides, and high volume workloads where speed matters.
Good first projects
Teams often start Sonnet 5.5 on code review and small bug fixes, drafting reports and slide decks, customer support agents, and research summaries over long documents. Its 1 million token context lets it read a whole codebase section or a large contract set in one request, and its lower price makes it a practical default for apps with many users.
How it compares
Its price matches OpenAI's GPT-6.1 Sol per token, though GPT-6.1 Sol has a cheaper cached input rate. Within Anthropic's lineup, step up to Claude Opus 5.5 for harder work or down to Claude Haiku 5.5 for bulk tasks. Our Claude Fable vs Opus vs Mythos guide covers the whole family, and the release timeline lists every launch.