Claude Sonnet 5.5 Claude Sonnet 5.5 is Anthropic’s latest midsize model, a faster and more cost-efficient complement to Claude Opus 5.5. It delivers up to 30% faster performance and lower token usage for typical workloads while matching or approaching Opus-level results on coding, agentic, and knowledge-work benchmarks. The model features a 1-million-token context window, adaptive thinking, and is available immediately on Claude.ai, the Claude API, Amazon Bedrock, Google Cloud, and Microsoft Foundry at $2 per million input tokens and $10 per million output tokens.