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Sprint projectOct 26, 2026

Do collusion probes generalise? Prompt confounds in NARCBench

Joe de Souza

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

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I investigated HELIOS, an activation-probe for detecting collusion. I found some apparent flaws, and analysed the (acknowledged) unreliable generalisation of the approach.

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  1. Good: Great use of counterfactual interventions ie holding behavior constant while modifying harmless prompt features. Isolated a plausible shortcut used by the benchmark. Strong methodological results.

    Weakness: Potential overgeneralization from deficiencies of one probe/benchmark to activation-based collusion detection more broadly. Prompt dependence doesn't necessarily prove the probe never detects real collusion representations.

    Recommendation: Leverage independently verified collusive outcomes (successful coordination rather than labels from LLM judge intentions), reproduce prompt-confound findings across other models, and test the full HELIOS pipeline. Tighten the distinction between failure to detect collusive intent and failure to detect demonstrated collusion.

Cite this project

@misc{souza2026collusion,
  title = {{Do collusion probes generalise? Prompt confounds in NARCBench}},
  author = {Joe de Souza},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/do-collusion-probes-generalise-prompt-confounds-in-narcbench-70ro}},
  url = {https://apartresearch.com/sprints/projects/do-collusion-probes-generalise-prompt-confounds-in-narcbench-70ro}
}

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