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Sprint projectOct 26, 2026

Cartels Under Model Replacement: Does a Language-Model Cartel Survive a Firm Swap?

Vatsal Kumar · Team Vatsal Kumar (solo)

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

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Language-model pricing agents can hold prices above the competitive level, and the model behind a deployed agent is often replaced. In a repeated three-firm pricing game, we ask whether a cartel-like price level survives when a firm is swapped mid-run. We save each run at round 30 and replay the rest in paired branches. In four models, a fresh copy or a model from another family left the price index essentially unchanged (-0.005 to +0.060), while a scripted undercutter lowered it by 0.05 to 0.30. Cutting messages while a fresh copy joined lowered it by 0.22 to 0.33. Results are conditional on a gate and use small samples.

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Cite this project

@misc{kumar2026cartels,
  title = {{Cartels Under Model Replacement: Does a Language-Model Cartel Survive a Firm Swap?}},
  author = {Vatsal Kumar},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/cartels-under-model-replacement-does-a-languagemodel-cartel-survive-a-firm-swap-hw05}},
  url = {https://apartresearch.com/sprints/projects/cartels-under-model-replacement-does-a-languagemodel-cartel-survive-a-firm-swap-hw05}
}

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