Deleting old agent turns can preserve effectiveness but raises real cost once prompt caching is counted
AspireAI community · arXiv
A study of 42 trajectory-reduction configurations across 9,400 runs of two agents on SWE-bench Verified finds that deleting large amounts of earlier reasoning content can leave overall effectiveness intact, but only if the deletion is delayed rather than applied immediately. Agents typically compensate for removed content by re-fetching it, which raises turn counts and token counts, so token savings alone overstate the benefit. Under flat pricing, estimated cost fell in 26 of 42 evaluations, but under a caching-aware pricing model none of the 42 came out cheaper, because shortening the trajectory breaks the cached prefix that would otherwise be billed at a lower rate. The practical takeaway is that context-window management has to be judged against realistic cached pricing, not raw token counts.
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