Reported Sonnet 5.5 speed and cost improvements

Willison quotes Anthropic’s claim that Sonnet 5.5 "runs 30%+ faster, and costs up to 30% less for most work". He writes that it is priced the same as Sonnet 5, "but appears to beat it on every benchmark, and should be cheaper to run as well".

Simon Willison·Published Sep 28, 2026

Behind the viewpoint

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Claude Sonnet 5.5

Original excerpt

Claude Sonnet 5.5 . New Sonnet model from Anthropic today. They say it "runs 30%+ faster, and costs up to 30% less for most work" - it's priced the same as Sonnet 5 but appears to beat it on every benchmark, and should be cheaper to run as well.

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