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Sprint projectOct 26, 2026London, United Kingdom

Undercover Agents: A Trusted Agent That Offers to Collude Partly Exposes and Deters Pact-Taking by LLM Agents

Razvan Sacara · Team Necessary Skew

Submitted to AI Collusion Research Sprint. Sprint projects are early-stage work by participants, not Apart Research publications.

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Report: Undercover Agents: A Trusted Agent That Offers to Collude Partly Exposes and Deters Pact-Taking by LLM Agents

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Can a trusted agent disrupt collusion between LLM agents by offering to collude?

In Zeng & Rudzicz's (2026) Liar's Bar harness, our scripted "sting" player privately offered one target a pact: neither would challenge the other. Who made the offer mattered. Qwen2.5-7B accepted from the game designer 493/500 times, but from the sting only 56/500. Claude Haiku 5.5 refused every explicit pact, yet accepted an indirect one 446/500 times. Accepted pacts showed in play: an audit flagged nearly all simulated accepters, with some false flags. An integrity notice cut Llama-3.1-8B's acceptance from 0.952 to 0.556.

So a sting exposes and deters pact-taking. But neither the notice nor the sting's private warning measurably weakened a pact already made with another player.

Scope: the hash-frozen preregistration covered Llama-3.1-8B and the Qwen and Claude offer replies. The Qwen and Claude live games, the audit and the replayed-pact tests are post hoc.

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Cite this project

@misc{sacara2026undercover,
  title = {{Undercover Agents: A Trusted Agent That Offers to Collude Partly Exposes and Deters Pact-Taking by LLM Agents}},
  author = {Razvan Sacara},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/undercover-agents-a-trusted-agent-that-offers-to-collude-partly-exposes-and-deters-pacttaking-by-llm-agents-0unb}},
  url = {https://apartresearch.com/sprints/projects/undercover-agents-a-trusted-agent-that-offers-to-collude-partly-exposes-and-deters-pacttaking-by-llm-agents-0unb}
}

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