Claude Sonnet 5 is positioned as the next step in Anthropic's Sonnet lineage and ships as a drop-in upgrade for the previous Sonnet generation, carrying the API identifier claude-sonnet-5. The launch centers on a behavior change rather than a new external architecture: adaptive thinking is on by default, replacing the older path where users manually requested extended reasoning. Requests that fall back to manual extended thinking now return an error, and the model also enforces default sampling behavior, rejecting non-default values for temperature, top_p, and top_k with a 400 error so that output style stays consistent across deployments.

For practical use, Claude Sonnet 5 is aimed at long-context, agentic workloads. It operates over a single the cataloged API limit context window that is both the default and the maximum, with no smaller variant, and produces up to the cataloged API limit output tokens per request. It inherits the broader Sonnet platform feature set and adds browser-use and a stable computer-use toolset that were not available on the prior Sonnet, opening up richer multi-step automation. Early third-party commentary from Endor Labs frames it as strong on functional coding tasks, more uneven on security outcomes, and notably candid about its own limitations, suggesting it is best matched to teams that can pair its tool breadth with their own safety review.