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Sprint projectOct 26, 2026

The Evidence Is in the Votes: LLM Monitors Mostly Miss Collusion That a One-Line Rule Catches

Reece Akana · Team Chillarin

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

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Report: The Evidence Is in the Votes: LLM Monitors Mostly Miss Collusion That a One-Line Rule Catches

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Can LLM monitors detect collusion among AI agents from the record of their interaction?

What I did: I had seven Llama 3.3 70B agents play a committee-vote game with private stakes, in which a secret colluding pair profits by vote trading: one member votes against its own small stake to secure its partner's large one. Across 160 matched games I compare no collusion, a private channel without instructions, naive colluders told to maximize their joint payoff, and competent colluders also given a vote-trading tip. Competent colluders traded at every opportunity, each gaining 0.43 points per round. LLM monitors saw public messages, actions, both, a said-versus-did table, and an upper-bound view adding private plans.

What I found: On each of the four observable views monitors were unable to detect collusion, with detection indistinguishable from chance (AUROC 0.44 to 0.60). However, giving them a one-line rule on actions (flagging votes against one's revealed payoff) allowed them to reach 0.86. The evidence is in the votes, and LLM monitors are unable to extract it.

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Cite this project

@misc{akana2026evidence,
  title = {{The Evidence Is in the Votes: LLM Monitors Mostly Miss Collusion That a One-Line Rule Catches}},
  author = {Reece Akana},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/the-evidence-is-in-the-votes-llm-monitors-mostly-miss-collusion-that-a-oneline-rule-catches-4ria}},
  url = {https://apartresearch.com/sprints/projects/the-evidence-is-in-the-votes-llm-monitors-mostly-miss-collusion-that-a-oneline-rule-catches-4ria}
}

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