Definition
Collusion means agents coordinate against their principals or against other agents. With LLM agents it emerges without any instruction. Self-interested agents that interact repeatedly and can model each other tend to drift into it.
- Pricing (Fish et al., 2024): agents told only “maximize profit” settle near the monopoly price. A one-sentence prompt change shifts how collusive they get. Antitrust law targets agreements, and here there is none.
- Auctions and markets: communication increases collusion. Firms divide markets without exchanging a message.
- Conventions (naming game): a population agrees on names without a leader and shows collective bias. A committed minority tips it past a critical mass (~2% to 25%).
- COLOSSEUM (2026) audits two signals: coalition advantage (what agents do) and an LLM judge (what they say). With a private channel, ~58% of 19 models colluded. The more an agent gains, the less collusive its talk sounds.
Appears in
- Lecture 11, pricing cartels
- Lecture 11, auctions and market division
- Lecture 11, conventions and tipping point
- Lecture 11, COLOSSEUM
- Lecture 11, talk vs. actions