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Sprint projectOct 23, 2026

Words vs Actions: An LLM Catches Broken Promises, Not Planned Lies

Het Kotadiya

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

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Report: Words vs Actions: An LLM Catches Broken Promises, Not Planned Lies

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LLM monitors often check whether an agent did what it promised. But a broken promise is not always a lie: an agent can honestly change its mind after hearing others. We tested whether an LLM detective can tell planned lies from honest changes of mind without seeing the agent’s private plan. Using Shi et al.’s Weakest Link game, we ran 50 games with Llama 4 Maverick (250 agents). From these we built a test set of 60: 30 planned liars, checked against their private plans and notes, plus 15 honest agents and 15 mind-changers. Sarvam 105B scored each agent from 0 to 100 using 4 kinds of evidence: its words, its final action, both, or its announced and final numbers. When the detective saw both what an agent said and what it did, it beat guessing (AUROC 0.79 and 0.71). But it could not tell liars from mind-changers (AUROC 0.47–0.63, and every 95% range included chance). It also flagged 11 of 15 honest mind-changers as liars. So say-vs-do monitoring catches broken promises, not planned lies, and it can wrongly accuse agents that honestly change their minds.

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Cite this project

@misc{kotadiya2026words,
  title = {{Words vs Actions: An LLM Catches Broken Promises, Not Planned Lies}},
  author = {Het Kotadiya},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/words-vs-actions-an-llm-catches-broken-promises-not-planned-lies-s2hc}},
  url = {https://apartresearch.com/sprints/projects/words-vs-actions-an-llm-catches-broken-promises-not-planned-lies-s2hc}
}

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