Agent Cost Drift: Measuring and Fixing Growing Memory File Token Costs

Short summary

The author discovered their scheduled article-writing agent's memory file grew from 500 to 7,360 tokens in a month, with entry size growing quadratically because each new entry must reference all prior topics. This 'agent cost drift' is a slow, invisible tax — no errors, no alerts, just steadily increasing per-run cost. The author wrote a measurement script to quantify the trend and proposes an archive-split fix: rolling recent entries plus a compact index for older ones.

• •Agent memory file grew from ~500 to ~7,360 tokens monthly with quadratic growth pattern
• •'Agent cost drift' is a class of bug: slow linear or quadratic cost increase with no error signal
• •Measurement script provided; proposed fix is an archive split with rolling window and compact index

Generated with AI, which can make mistakes.