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Sprint projectOct 26, 2026Cape Town

Watch the Price, Change the Payoff: Detecting and Breaking Tacit Collusion Between AI Pricing Agents

Giada Bertola, Justin Feldman · Team Maverick

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

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Report: Watch the Price, Change the Payoff: Detecting and Breaking Tacit Collusion Between AI Pricing Agents

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AI agents are starting to set prices, and they can collude without ever talking to each other. We ran 436 pricing games with AI sellers from nine model families, including Claude, GPT, Gemini, Grok and GLM. The sellers pushed prices above competitive levels with no communication channel.

A simple monitor that compares each seller’s price with the fair price, given what its rivals charge, caught 25 of 27 forming cartels before they locked in, with no false alarms. Because it needs only prices, it works on any vendor’s model.

The usual countermeasures failed. Undercover competitive agents didn’t break cartels, and hiding rivals’ prices didn’t help. Agents told there was no future still didn’t undercut. They seem to share a mistaken belief that high prices are best.

What worked was changing the payoff. A fee on prices above the fair level, switched on by the monitor’s warning, cut collusion from 0.36 to 0.08 and prevented every cartel in a pre-registered test (p = 0.05).

The result is a blueprint for anti-collusion software: watch prices, and make overpricing cost money. The main step before real-world use is estimating the fair price from real market data.

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  1. The most useful question at the heart of this project is, once agents start charging too much, what actually brings prices down? Comparing several approaches and being open about the ones that failed makes the fee result worth following up. A helpful next experiment would announce the fee without changing the payoff, to see whether the agents respond to the cost or just the warning. The detection results would also be easier to judge with early lock-ins included and false alarms shown separately for each control group, while keeping the distinction between high prices and a coordinated cartel clear.

Cite this project

@misc{bertola2026watch,
  title = {{Watch the Price, Change the Payoff: Detecting and Breaking Tacit Collusion Between AI Pricing Agents}},
  author = {Giada Bertola and Justin Feldman},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/watch-the-price-change-the-payoff-detecting-and-breaking-tacit-collusion-between-ai-pricing-agents-8vah}},
  url = {https://apartresearch.com/sprints/projects/watch-the-price-change-the-payoff-detecting-and-breaking-tacit-collusion-between-ai-pricing-agents-8vah}
}

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