Reading Between the Agents: Message and Action Evidence in Coordination Monitoring
Mahlet Molla, Lydia Lee · Team Decode
Submitted to AI Collusion Research Sprint. Sprint projects are early-stage work by participants, not Apart Research publications.
Monitoring multi-agent coordination requires weighing what agents say against what they do, not conflating evidence with intent. In a pilot study of a two-option game where the operator prefers option A, we first varied scripted sender messages and measured two language models' responses as receivers. Sonnet 4.6 chose the permitted but discouraged option B in 8/20 trials under a B-directed proposal, GPT-5.4-mini in 7/20 under an A-directed one; however, direction was bundled with wording. We then compared four monitors: message-only, action-only, combined, and combined with a checklist. Message-only and combined monitors reached AUROC 1.00 on the resolved subset, so combining evidence showed no gain. This reflects a ceiling, not equivalence, because the endpoint is post hoc and perfectly separable by template. These findings show how endpoint construction, evidence asymmetry, and prompt design can limit what a monitoring evaluation shows, and we offer two diagnostics, saturation and evidence-contract checks, for future benchmarks.

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@misc{molla2026reading,
title = {{Reading Between the Agents: Message and Action Evidence in Coordination Monitoring}},
author = {Mahlet Molla and Lydia Lee},
year = {2026},
month = oct,
note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
howpublished = {\url{https://apartresearch.com/sprints/projects/reading-between-the-agents-message-and-action-evidence-in-coordination-monitoring-9dpn}},
url = {https://apartresearch.com/sprints/projects/reading-between-the-agents-message-and-action-evidence-in-coordination-monitoring-9dpn}
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