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Sprint projectOct 25, 2026Cambridge

Reading Moves, Not Messages: Detecting Collusion Between LLM Agents

Josh Snow · Team Snow

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

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Report: Reading Moves, Not Messages: Detecting Collusion Between LLM Agents

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uence, a collusion detector that uses only agents' actions, on LLM agents (Gemma 4) playing Rock–Paper–Scissors with a private message channel. We replaced its fixed threshold with a permutation test, cutting false positives from up to 49% to 1–5%, and extended it to long histories and groups of colluders. It caught every colluding pair, including unprompted collusion, with no false flags, where correlation and an LLM judge failed. It also caught every LLM bid-rigging ring in an auction.

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Cite this project

@misc{snow2026reading,
  title = {{Reading Moves, Not Messages: Detecting Collusion Between LLM Agents}},
  author = {Josh Snow},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/reading-moves-not-messages-detecting-collusion-between-llm-agents-9mgg}},
  url = {https://apartresearch.com/sprints/projects/reading-moves-not-messages-detecting-collusion-between-llm-agents-9mgg}
}

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