Did They Collude or Just Agree? What Counts as Evidence of Collusion Among AI Reviewers

Two reviewers vouch for a claim, and the claim turns out to be false. Did they collude, or only agree? A shared source, copying, a persuasive proposer, and a shared incentive all leave the same records. I built a small review game to find out what can tell these causes apart. A proposer selects evidence, two reviewers endorse or reject, a decider approves, and an auditor reads the record later. Eight settings cover an honest baseline, four innocent causes, a chance to collude, talk without action, and a scripted pact. I fixed the hypotheses and tests before the data and ran one language model as the confirmatory test. Six more models followed with the same prompts, 288 plays each, as an exploratory check. Three results held for all seven. The private channel never made the decider approve more false claims; in two models it made fewer. Provenance data did not help the auditors, because they almost never accused an innocent record. A keyword auditor found my scripted pact and missed the pacts the models wrote in their own words. In the three models classified by hand, words did not predict actions. Of 108 classified records, one showed a pact that changed an action. Only an auditor that could compare the record with the same case played without the channel caught it. A real auditor has no such second record. Harm alone and messages alone are not evidence of collusion. Convincing evidence must link a plan to a change in action.