Tacit Collusion in LLM Bidders
48-session baseline · 2 models · 4 arms
- Conceived the study and built its auction harness: does letting LLM firms communicate raise prices? Four pre-registered arms: no channel, private notes, a shared workspace, an open message channel.
- Ran a pre-registered no-channel baseline of 48 sessions (2 models, 12 seeds, 50 rounds), each matched with a one-shot control. With history, DeepSeek V4.1 Flash bid about 1 to 2.3 below the Bayes-Nash bid by round 50 and GPT-6 Luna about 6 above it; neither control drifted.
- Merged a collaborator's shared-workspace and message-channel code, then built the private-notes control as a one-switch variant of it, with a log check that no prompt shows a firm the other's notes.
- Pre-registered two hypotheses in
configs/analysis.yamlbefore any session ran (paired exact sign-flip tests, Holm-corrected) and ran 24 GPT-6 Luna notes sessions. Analysis in progress.