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Sprint projectOct 26, 2026Seattle, WA, USA

Better Angels Have Their Limits: Collusion in Mixed LLM Pricing Games

Jim Kleban · Team Super Colluders

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

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150 words, with four words added and “may lowers” corrected:

Market-based pricing games are studied as testbeds for collusive behavior between LLM agents. Self-play outcomes vary across models, from competitive pricing to sustained high prices and above-Nash profits. We find that Claude Haiku 5.5 is a ‘better angel’ in self-play, pricing competitively, while Gemini 3.8 Flash sustains elevated prices. In mixed games, however, Haiku and Gemini sustain high prices and above-Nash profits for both sellers in three of five fresh games. In continuations of high-priced Gemini markets, replacing one seller with Haiku lowers the remaining seller's prices in all five markets relative to a Gemini control. While this removes about three-quarters of the remaining seller's average price elevation above Nash, some runs still sustain high prices and above-Nash profits for both sellers. Competitive self-play therefore does not ensure competitive mixed play, and switching to a ‘better angel’ LLM has limits. It may lower prices but does not reliably restore competition.

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Cite this project

@misc{kleban2026better,
  title = {{Better Angels Have Their Limits: Collusion in Mixed LLM Pricing Games}},
  author = {Jim Kleban},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/better-angels-have-their-limits-collusion-in-mixed-llm-pricing-games-706a}},
  url = {https://apartresearch.com/sprints/projects/better-angels-have-their-limits-collusion-in-mixed-llm-pricing-games-706a}
}

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