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Sprint projectOct 26, 2026Online | Tampa, FL, USA

Replacement or Announcement? A Matched-Notice Pilot on LLM Price Collusion

Shivani Jagannatham · Team Esc the Cartel

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

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When AI pricing agents keep prices high, the obvious fix is to replace one of them. I tested whether that works with two Gemini sellers in a simulated market (LLMCartel). These agents have no memory beyond the price history in their prompt, so a restart only exists if you tell them, and that notice can move prices by itself. To separate the two, I continued one high-price history three ways. In the first nothing changed, in the second the same model got a restart notice, and in the third one seller got the same notice and was switched to an older Gemini model.

The new model kept prices high, exactly like no change. The notice alone made the original model cut its price from 1.92 to 1.43 and set off a price war. Rerunning that round 20 times, the cut came back in 4 of 20 runs and never happened without the notice or with the new model. I also found both models start at the high price with no history (40 of 40). The takeaway is that replacement studies need a notice-only control. This is one history, so the results are exploratory.

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  1. Separating the effect of replacing a model from the effect of announcing it is a promising idea, but the findings need validation across more independent market histories. I sometimes found the paper harder to follow, especially the distinction between the interrupted original study and the exploratory follow-up experiments.

Cite this project

@misc{jagannatham2026replacement,
  title = {{Replacement or Announcement? A Matched-Notice Pilot on LLM Price Collusion}},
  author = {Shivani Jagannatham},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/replacement-or-announcement-a-matchednotice-pilot-on-llm-price-collusion-hhaj}},
  url = {https://apartresearch.com/sprints/projects/replacement-or-announcement-a-matchednotice-pilot-on-llm-price-collusion-hhaj}
}

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