Anthropic Releases Claude Sonnet 5.5

Anthropic has released Claude Sonnet 5.5, the second model in its Claude 5.5 family, featuring 30% faster output generation and up to 30% lower costs compared to its predecessor. The model maintains Sonnet 5's pricing structure at $2 per million input tokens and $10 per million output tokens, while introducing advanced cybersecurity safeguards previously reserved for flagship models.

Anthropic released Claude Sonnet 5.5 on September 28, 2026, positioning it as a faster and more cost-effective complement to the previously launched Claude Opus 5.5. The model generates outputs over 30% faster and costs up to 30% less per task while maintaining the same pricing tier as its predecessor-$2 per million input tokens and $10 per million output tokens.

Sonnet 5.5 is optimized for well-scoped everyday tasks, including bug fixing and document creation. Anthropic describes it as particularly strong at producing polished documents, slides, and spreadsheets, while also offering enhanced design capabilities. The company highlights that early testers found it to be a more effective collaborator than Sonnet 5, with clearer writing suited for rapid iteration on less complex tasks.

A significant advancement in this release is the inclusion of frontier-style cybersecurity safeguards-a feature that was previously exclusive to Anthropic's most capable models. Claude Sonnet 5.5 is the first Sonnet model to ship with cyber protection mechanisms and classifiers designed to prevent reasoning extraction, addressing emerging security concerns in the AI field. The model achieves a score of 70.6% on the Terminal-Bench 4.0 agentic coding test, comparing favorably to Opus 5.5's 66.4% on its highest effort setting.

Claude Sonnet 5.5 is available across all major platforms including Amazon Web Services, Google Cloud, and Microsoft Azure under the model ID claude-sonnet-5-5. The release follows Anthropic's September 22 launch of Claude Opus 5.5 and precedes the anticipated arrival of Claude Haiku 5.5 in the coming weeks, signaling the company's accelerated push to expand its Claude 5.5 family across performance tiers.