Anthropic has launched Claude Sonnet 5.5, the second model in its Claude 5.5 family and a direct upgrade to Sonnet 5. The company positions it as its fastest Sonnet yet, built for well-scoped everyday work such as bug fixes, documents, slides, spreadsheets, and design. It is meant to complement Opus 5.5, which remains the stronger choice for complex, open-ended jobs that require sustained judgment, including demanding coding, longer assignments, visual understanding, slide creation, and UI design.
Introducing Claude Sonnet 5.5, the second model in the Claude 5.5 family.
— Claude (@claudeai) September 28, 2026
It’s a clear upgrade over Sonnet 5, runs more than 30% faster, and costs up to 30% less for most work. pic.twitter.com/UvXD8mDTF1
Anthropic says Sonnet 5.5 produces output more than 30% faster and can cost up to 30% less per task for most workloads because it requires fewer tokens. Per-token pricing remains unchanged at $2 per million input tokens, $10 per million output tokens, $0.20 per million cache-read tokens, and $2.50 per million cache-write tokens.
The reported benchmark gains are substantial. Sonnet 5.5 scored 70.6% on Terminal-Bench 4.0, compared with 10.3% for Sonnet 5, and 55.5% on CursorBench 4.0, compared with 34.1%. At Max effort, it reached 46.2% on FrontierCode 1.1 Main versus 42.4% for its predecessor. Anthropic also says the model is close to Opus 5.5 on GDPval-AA knowledge work and recorded an 80.1% partial score on OSWorld 2.1, up from 57.0% for Sonnet 5.
Sonnet 5.5 also has a knack for design. It adds polish to user interfaces and follows templates to create slides that need minimal editing. pic.twitter.com/LtWOFp4coo
— Claude (@claudeai) September 28, 2026
Claude Sonnet 5.5 is available across all platforms, including AWS, Google Cloud, and Microsoft Azure. Developers can select it on the Claude Platform with the model ID claude-sonnet-5-5, and zero data retention is available. Default effort is Medium in Claude Code and Claude apps, while Claude Platform defaults to High. Users can adjust effort to trade speed against cost. Those migrating from Sonnet with thinking turned off must switch to the new between_tools setting.
This is also the first Sonnet release with cyber safeguards and fallback behavior for higher-risk requests, following the approach used for Opus 5.5. Anthropic says biology safeguards remain the same as in Sonnet 5, while new classifiers target reasoning extraction and preserved thinking has been expanded. The company says the narrow controls do not affect routine software development or most life sciences work.
The release fills out Anthropic’s Claude 5.5 lineup with a faster, lower-cost option for everyday tasks while keeping Opus at the top for harder work. Haiku 5.5 is due in the coming weeks, extending the family with another tier.
