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Sprint projectOct 26, 2026New York

Where Prices Start Matters More Than What Sellers Say: Testing Anti-Collusion Remedies on Pressured LLM Sellers

Jianing Fan, Emeric Chang, Santiago Ballestas, Sophie Zhang · Team CAIAC AM

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

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AI pricing agents can sustain prices above competitive levels. We test which remedies reduce this pricing at the least cost. Using the double-auction market of Agrawal et al. (2025), we studied three GPT-4.1 sellers instructed by their CEO to keep margins high. This produced a stable control with an ask index of 0.66, where 0 represents the competitive price and 1 the cartel price. We compared 11 remedies with this control using matched seeds (14 conditions × 5 seeds, 70 runs). Remedies included communication bans and caps, an unenforced warning, monitoring with varying message access and enforcement, and a scripted price-cutting rival. For each remedy, we measured how much elevated pricing it removed and what it cost in lost trades and messages read. Sellers maintained their initial asking prices. Starting asks at the competitive price eliminated elevated pricing (index −0.07), the only effect that survived correction for multiple tests in our primary analysis. Restricting or monitoring communication had limited effects: a ban removed 16% of elevated pricing, caps almost none, and four of five monitors 11%–21%. An unenforced warning removed 28%. No remedy reduced trade. In this small, single-model market, high prices reflected sellers’ starting prices instead of their communication. Oversight of AI pricing agents should therefore examine their objectives and price anchors alongside their messages.

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  1. Great response to question 3 with an intriguing finding (anchoring). Would be great to add more seeds, one or more models. Appreciate the extensive appendix but parts can be outsourced to companion repo.

Cite this project

@misc{fan2026where,
  title = {{Where Prices Start Matters More Than What Sellers Say: Testing Anti-Collusion Remedies on Pressured LLM Sellers}},
  author = {Jianing Fan and Emeric Chang and Santiago Ballestas and Sophie Zhang},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/where-prices-start-matters-more-than-what-sellers-say-testing-anticollusion-remedies-on-pressured-llm-sellers-pgto}},
  url = {https://apartresearch.com/sprints/projects/where-prices-start-matters-more-than-what-sellers-say-testing-anticollusion-remedies-on-pressured-llm-sellers-pgto}
}

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