Abstract
Large language models (LLM) deployed as autonomous pricing agents may sustain supracompetitive prices through tacit coordination. We develop a causal graph divergence framework that separately measures structural faithfulness and intent faithfulness of LLM pricing agents in Bertrand competition. Across nine LLMs under duopoly and triopoly conditions, collusive behavior and chain-of-thought (CoT) faithfulness dissociate along both dimensions: the most collusive model accurately reports cooperative intent yet reasons structurally unfaithfully, while the most structurally faithful model sustains supra-Nash pricing under both market structures. These findings establish that CoT monitoring alone cannot serve as a standalone safeguard against algorithmic collusion.
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Cite this article
APA 7
Lee, D., & Park, H. (2026). Faithful yet Collusive: Why Chain-of-Thought Monitoring Cannot Detect Collusion in LLM Pricing Agents under Oligopolistic Competition. https://omanscience.com/en/articles/faithful-yet-collusive-why-chain-of-thought-monitoring-cannot-detect-collusion-in-llm-pricing-agents-under-oligopolistic-competition
MLA 9
Lee, Dohun, and Hyunwoo Park. "Faithful yet Collusive: Why Chain-of-Thought Monitoring Cannot Detect Collusion in LLM Pricing Agents under Oligopolistic Competition." https://omanscience.com/en/articles/faithful-yet-collusive-why-chain-of-thought-monitoring-cannot-detect-collusion-in-llm-pricing-agents-under-oligopolistic-competition.
Chicago (author–date)
Lee, Dohun, and Hyunwoo Park. 2026. "Faithful yet Collusive: Why Chain-of-Thought Monitoring Cannot Detect Collusion in LLM Pricing Agents under Oligopolistic Competition." https://omanscience.com/en/articles/faithful-yet-collusive-why-chain-of-thought-monitoring-cannot-detect-collusion-in-llm-pricing-agents-under-oligopolistic-competition.
Harvard
Lee, D. and Park, H. (2026) 'Faithful yet Collusive: Why Chain-of-Thought Monitoring Cannot Detect Collusion in LLM Pricing Agents under Oligopolistic Competition', Available at: https://omanscience.com/en/articles/faithful-yet-collusive-why-chain-of-thought-monitoring-cannot-detect-collusion-in-llm-pricing-agents-under-oligopolistic-competition.
Vancouver
Lee D, Park H. Faithful yet Collusive: Why Chain-of-Thought Monitoring Cannot Detect Collusion in LLM Pricing Agents under Oligopolistic Competition. https://omanscience.com/en/articles/faithful-yet-collusive-why-chain-of-thought-monitoring-cannot-detect-collusion-in-llm-pricing-agents-under-oligopolistic-competition
IEEE
D. Lee, and H. Park, "Faithful yet Collusive: Why Chain-of-Thought Monitoring Cannot Detect Collusion in LLM Pricing Agents under Oligopolistic Competition," https://omanscience.com/en/articles/faithful-yet-collusive-why-chain-of-thought-monitoring-cannot-detect-collusion-in-llm-pricing-agents-under-oligopolistic-competition.