Replacing the Agent Doesn't Reset the Price: LLM Pricing Collusion Lives in the Record

The real and fabricated record transplants provide useful evidence that inherited history affects later pricing. The contrast between a falling profit index and persistently high consumer prices is an important warning about evaluating remedies with seller profits alone. Please revise the claim that replacement leaves coordination unchanged: the fresh-Qwen confidence interval includes a meaningful reduction, and a nonsignificant test is not an equivalence test. Report final-window outcomes separately from ever crossing a rolling threshold; the latter can label temporary recovery as persistence. The Phi-4 experiment supports record sensitivity, but not replication of profitable collusion. A no-notes, record-wiped contrast against the otherwise identical no-notes, record-kept arm would isolate the record intervention more directly. Follow-up should include all base games, longer branches, preregistered equivalence margins, and direct consumer-surplus outcomes. The absent punishment response limits the enforcement interpretation; the inherited price effect remains economically relevant. Keppo et al., On the Fragility of AI Agent Collusion, already distinguishes size diversity from algorithm-type diversity. Your contribution is mid-game replacement after a saved history, not heterogeneity generally. A Phi-4 replacement should not be read as evidence that replacing an LLM with another algorithm class would also fail.

This paper provides useful evidence that replacing a pricing agent can leave high prices in place when the newcomer inherits the market record. The checkpoint-and-branch design, real and fabricated record transplants, and results with Phi-4 strengthen the finding that inherited records influence subsequent pricing. The divergence between seller profits and prices after record-wiping is particularly valuable: it illustrates why a lower profit-based collusion index is not enough to establish consumer benefit.

The main revision should concern the strength of two conclusions. The price estimate after wiping is uncertain, so “no reliable price reduction was observed” is better supported than “consumers receive no benefit.” The recommendation to target records rather than models is also too exclusive. Phi-4 newcomers change prices, showing that model choice still matters. The evidence supports considering market records alongside model behavior.

These points can be addressed through more precise wording. Overall, the main experiments are convincing, and the paper offers a useful lesson for designing and evaluating interventions.

This project tests whether replacing LLM pricing agents resets prices. The checkpoint-and-branch design, with transplanted real and fabricated records, gives clean evidence that the shared price record sets the price level. In addition, the observation that the standard profit-based index would call record-wiping a success while consumers pay more is a useful lesson for evaluating remedies. However, the high prices here are mostly overpricing rather than collusion: agents open well above the monopoly price, price near +2.1 with no record, never respond to a forced cut, and Phi-4 never coordinates profitably. The title’s “collusion” is therefore inconsistent with the paper’s own conclusion. Replicating within arms and adding a noise floor would strengthen the conclusions.