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Sprint projectOct 26, 2026Detroit

How much coalition advantage does one binary message buy?

Shashwat Bhatia · Team Decode

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

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Does a coalition of agents do better with one binary message per episode than with none? I added a one bit budget to the Colosseum Jira task and tested it on four models. A mediator lets one sender post one message, 0 or 1, in one fixed slot. The bit tells the partner which of two joint plans fits a hidden draw that only the sender can see. I compare one bit against a silent channel, paired by seed, with a shuffled bit as the content control and free talk as the positive control. The answer is inconclusive on every model I could judge. On Qwen2.5-7B-Instruct, over 30 paired games per arm, one bit beat silence by +0.49 points of coalition advantage (95 percent interval -3.67 to +4.98). On Qwen2.5-14B-Instruct-AWQ the gap was +0.81 (-5.36 to +6.38). The one clean result is on 14B, where the real bit beat the shuffled bit by +4.98 (+0.06 to +10.22). The 32B and GPT-5 mini batches failed the positive control, so they count as description only. The gate itself held in all 280 audited runs, and no arm harmed the other players.

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Cite this project

@misc{bhatia2026much,
  title = {{How much coalition advantage does one binary message buy?}},
  author = {Shashwat Bhatia},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/how-much-coalition-advantage-does-one-binary-message-buy-fn6v}},
  url = {https://apartresearch.com/sprints/projects/how-much-coalition-advantage-does-one-binary-message-buy-fn6v}
}

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