Claude Sonnet 5.5

Claude Sonnet 5.5 is a proprietary language model from Anthropic, released on Sep 28, 2026.

At $2 input and $10 output per million tokens, it ranks #20 of 38 for input price, placing it mid-range on input cost.

Its context window of 1.0M tokens ranks #11 of 39 for context depth in this dataset.

It targets coding, agents, reasoning workloads.

Released Sep 28 2026. Anthropic describes it as the best combination of speed and intelligence in the current lineup (comparative latency: fast). Adaptive thinking is on by default (default effort high); the lowest setting, between_tools, turns off up-front thinking. Five breaking changes affect code written for Sonnet 5: up-front thinking is turned off with between_tools, forced tool use returns an error, thinking blocks are tied to the model and conversation, computer_20251124 is not accepted on the Claude API and Google-managed Google Cloud, and the advisor tool rejects Opus 4.8, Opus 4.7, Sonnet 5 and Haiku 5.5 as advisors. Setting temperature, top_p or top_k returns a 400 error. Text and image input, up to 300K output on the Batch API with the output-300k-2026-03-24 beta header. API identifier claude-sonnet-5-5 (anthropic.claude-sonnet-5-5 on Bedrock), reliable knowledge cutoff June 2026, retirement not sooner than Sep 28 2027. Source: https://platform.claude.com/docs/en/models/sonnet-5-5/overview (checked 2026-10-23).