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Sprint projectOct 25, 2026

Collusion Detectors See Shared Secrets, Not Collusion

Sidhant Mahi · Team LUNA

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

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We tested whether information-theoretic statistics, including Bonjour et al.’s pairwise net influence, can identify a colluding pair in repeated Rock–Paper–Scissors. We ran them on scripted agents, Qwen2.5-3B and Claude Haiku 5.5, and compared them against action correlation and an LLM judge. We found that these detectors measure shared hidden information, not collusion. They miss collusion through public signals, and net influence is biased and degenerate in short games. In our LLM pilot the seeded colluders never actually coordinated, so every statistic was at chance. The LLM judge was below chance, because it mistook honest herding for collusion.

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Cite this project

@misc{mahi2026collusion,
  title = {{Collusion Detectors See Shared Secrets, Not Collusion}},
  author = {Sidhant Mahi},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/collusion-detectors-see-shared-secrets-not-collusion-3apy}},
  url = {https://apartresearch.com/sprints/projects/collusion-detectors-see-shared-secrets-not-collusion-3apy}
}

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