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Sprint projectOct 26, 2026Bristol

What does “communication off” turn off? A preregistered decomposition of a communication ablation in an LLM double auction

Warren Smith · Team OMEGA

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

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Studies of collusion among LLM agents often compare markets with seller communication switched on and off. We tested what that switch actually changes in an LLM double-auction benchmark by separating message delivery from the accompanying prompt and output-interface changes.

In a preregistered 30-market experiment, the primary effect of removing the remaining communication interface after delivery was withheld was not detected: +$21.1 in buyer-surplus loss [−10.7, 57.2]. A second-model run was also inconclusive. In a further 40-market decomposition, removing the empty-inbox section increased buyer-surplus loss by $16.8 [4.4, 33.1], while removing the request to write messages was not detected.

The benchmark’s positive control was not met (0/30 communication-on markets), so we make no claim that collusion occurred. The result is instead methodological: a “communication off” switch can bundle message removal with changes to what agents see and are asked to do. We recommend reporting a delivery-withheld control and the exact prompt differences between experimental arms.

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Cite this project

@misc{smith2026communication,
  title = {{What does “communication off” turn off? A preregistered decomposition of a communication ablation in an LLM double auction}},
  author = {Warren Smith},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/what-does-communication-off-turn-off-a-preregistered-decomposition-of-a-communication-ablation-in-an-llm-double-auction-kojm}},
  url = {https://apartresearch.com/sprints/projects/what-does-communication-off-turn-off-a-preregistered-decomposition-of-a-communication-ablation-in-an-llm-double-auction-kojm}
}

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