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Sprint projectOct 26, 2026

Noticing the Move, Missing the Player: LLM Agents Detect Behavioral Shifts but Not Peer Swaps

V S Siva Kumar Lakkoju, Kaustubh Gupta, Gagana M D · Team SwapSwapGo

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

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Report: Noticing the Move, Missing the Player: LLM Agents Detect Behavioral Shifts but Not Peer Swaps

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Can agents detect when a peer is replaced midway through a social dilemma? We tried three multi-agent settings to answer this question: Diner’s Dilemma, Public Goods Game (PGG) and RepeatedJira environment. In the Diner’s Dilemma and Public Goods Game (PGG), agents played repeated social dilemmas before a peer one of them was swapped while in RepeatedJira, a monitor secretly took over one seat in an instructed collusion setup. Agents generally reacted more clearly to changes in a peer’s behaviour than to the fact of replacement. In Diner’s Dilemma, agents with or without memory of the history could not detect any swap despite an LLM-judge identifying a change in the writing style after swap. In the PGG, silent swaps produced no positive direct replacement reports in the tested conditions, while responses to a visible seat-label change depended on the base model. Peers also distinguished free-riding behaviour from control play, with behavioural-probe AUCs of 0.915 in the five-player design and 0.944–0.984 in two three-player runs. In RepeatedJira, the remaining colluder continued to request coordination when the monitor stopped helping, but did not identify the monitor as a replacement.

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Cite this project

@misc{lakkoju2026noticing,
  title = {{Noticing the Move, Missing the Player: LLM Agents Detect Behavioral Shifts but Not Peer Swaps}},
  author = {V S Siva Kumar Lakkoju and Kaustubh Gupta and Gagana M D},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/noticing-the-move-missing-the-player-llm-agents-detect-behavioral-shifts-but-not-peer-swaps-uf7r}},
  url = {https://apartresearch.com/sprints/projects/noticing-the-move-missing-the-player-llm-agents-detect-behavioral-shifts-but-not-peer-swaps-uf7r}
}

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