Anthropic says Sonnet 5.5 costs up to 30% less per task than Sonnet 5 — but independent testing at the limits tells a different story. Benchmarking firm Artificial Analysis, running Sonnet 5.5 at max effort, found it used about 193,000 output tokens per task, roughly 60% more than Opus 5.5 — making it more expensive per task than Sonnet 5 when pushed to the ceiling. CodeRabbit's VP of AI separately confirmed Sonnet 5.5 spends fewer output tokens than Sonnet 5 in normal code review.

Anthropic itself warns effort is a tradeoff: low effort may skip verification, while xhigh or max can add unsolicited review work. The practical read is that Sonnet 5.5 is cheaper at the default Medium/High settings most users run, but cost-hungry max-effort runs can erase the savings entirely. It's also the first Sonnet to launch with Anthropic's stricter cyber safeguards — high-risk requests in some apps fall back to Sonnet 5.