Claude Sonnet 5.5 is available through the Claude API and its cloud partners. Applications moving from Sonnet 5 face changes to thinking blocks and forced tool selection; some older settings return errors with the new model. Token pricing is unchanged. The release therefore brings an integration change for developers alongside access to the new model.
Anthropic says Claude Sonnet 5.5 is available through its Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry. Its API identifier is claude-sonnet-5-5. The company says the tokenizer and token price schedule match those of Sonnet 5. The release provides current access for developers, rather than only a future plan. Anthropic’s comparisons of speed and performance with the previous model are based on its own testing.[1], [2]
Anthropic’s migration guide lists five breaking changes for applications using Sonnet 5. The older setting that disables thinking entirely returns an error with the new model, while adaptive thinking is enabled by default. Tool-choice settings that force a particular tool also fail; automatic selection remains available. An application moving to The new model therefore has to review its tool-call settings as well as changing the model identifier.[1]
Thinking blocks are tied to the model and conversation that created them, and cannot always be reused after an application switches models. On the Claude API and Google Cloud, the older computer_20251124 computer-use tool is rejected with the new model; Anthropic directs developers to the newer toolset. It describes a different compatibility position for Amazon Bedrock. Progress text generated between tool calls also moves into thinking blocks, a change that can affect what a streaming client displays.[1]
