Claude Sonnet 5.5

Anthropic released Claude Sonnet 5.5 on September 28, 2026, according to a post by Simon Willison on his website. Willison reported that Anthropic describes the new model as running “30%+ faster” and costing “up to 30% less for most work” compared with its predecessor. He noted the model is priced the same as Claude Sonnet 5, and wrote that it appears to beat that prior version on every benchmark, while also being cheaper to run.

Willison’s post included a link to sample outputs, described as pelican drawings, hosted on a tool he built for rendering markdown as SVG, pointing to a gist he had published.

Willison did not provide a list of specific benchmarks or figures beyond the percentage claims attributed to Anthropic, nor did he elaborate on the criteria used to reach the “beats it on every benchmark” observation. His post centered on the pricing and speed claims, the benchmark comparison, and the linked pelican image samples, without further technical detail in the excerpt available.