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Sprint projectOct 25, 2026Coimbatore

Collusion Lives in Memory: Localising and Stress-Testing Tacit Coordination Between LLM Agents

Sujit Narrayan M, Shalini Ghosh · Team NextGen

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

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Report: Collusion Lives in Memory: Localising and Stress-Testing Tacit Coordination Between LLM Agents

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Audits can show that LLM agents collude, but a defender needs to know where the coordination is stored. Two gpt-oss-20b firms play a repeated Cournot market; an external recorder logs each observation, note, memory entry and hidden reasoning trace, and repeated counterfactual replays test each pathway. Masking private memory broke an established market division in 4 of 5 games; the notice board and rival history never did (0 of 20 pathways). Single-replay audits were wrong for 5 of 9 flagged pathways. Sanitising memory left the collusive rule intact, and the sanitised notes transmitted it: fresh firms given them divided the market with new rivals in 6 of 6 games, versus 0 of 6 with non-colluders’ notes (p = 0.002). A monitoring notice did not deter division, but 43% of monitored firms’ hidden reasoning discussed detection (vs 1%). Auditors should verify carriers by repeated intervention and read behaviour, not self-reports.

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Cite this project

@misc{m2026collusion,
  title = {{Collusion Lives in Memory: Localising and Stress-Testing Tacit Coordination Between LLM Agents}},
  author = {Sujit Narrayan M and Shalini Ghosh},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/collusion-lives-in-memory-localising-and-stresstesting-tacit-coordination-between-llm-agents-nyi5}},
  url = {https://apartresearch.com/sprints/projects/collusion-lives-in-memory-localising-and-stresstesting-tacit-coordination-between-llm-agents-nyi5}
}

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