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Sprint projectOct 26, 2026

Price Afterimage: Markets Remember What Agents Forget

Noel Thomas, Praveen Shukla · Team Afterimage

Submitted to AI Collusion Research Sprint. Sprint projects are early-stage work by participants, not Apart Research publications.

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When an AI pricing agent takes over a running market, it inherits a price history it did not write. Does that history set its price? We plant the opening prices in a two-firm market where stateless language-model agents see only the last 20 rounds, then measure the price afterimage: the share of the planted price gap still charged once no prompt shows it. For Qwen3-14B, 0.84 of the gap remains 80 or more rounds later (pre-registered; 0.79 on fresh seeds). The agents forget the plant; the market they write together does not. Replace one agent with a scripted best responder and the afterimage vanishes (0.001): the two agents carry it by tracking each other's prices. In the market of a recent study (Lee, 2026), the opening alone flips two of its four significant model rankings, so a cold-start ranking partly reflects history, not just the model. A one-line best-response hint brings prices to the competitive level. Deployers should audit the price histories their agents inherit.

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Cite this project

@misc{thomas2026price,
  title = {{Price Afterimage: Markets Remember What Agents Forget}},
  author = {Noel Thomas and Praveen Shukla},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/price-afterimage-markets-remember-what-agents-forget-0i3o}},
  url = {https://apartresearch.com/sprints/projects/price-afterimage-markets-remember-what-agents-forget-0i3o}
}

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