Probing the Limits of the Lie Detector Approach to LLM Deception

• URL: http://arxiv.org/abs/2603.10003v1
• Date: Mon, 16 Feb 2026 19:01:55 GMT
• Title: Probing the Limits of the Lie Detector Approach to LLM Deception
• Abstract summary: This paper experimentally investigates whether large language models can deceive without producing false statements.<n>It is shown that some models reliably deceive by producing misleading non-falsities, particularly when guided by few-shot prompting.<n>It is proposed that future work should incorporate non-lying deception in dialogical settings into probe training to more directly target the conceptual constituents of deception.
• Score: 0.0
• License: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Abstract: Mechanistic approaches to deception in large language models (LLMs) often rely on "lie detectors", that is, truth probes trained to identify internal representations of model outputs as false. The lie detector approach to LLM deception implicitly assumes that deception is coextensive with lying. This paper challenges that assumption. It experimentally investigates whether LLMs can deceive without producing false statements and whether truth probes fail to detect such behavior. Across three open-source LLMs, it is shown that some models reliably deceive by producing misleading non-falsities, particularly when guided by few-shot prompting. It is further demonstrated that truth probes trained on standard true-false datasets are significantly better at detecting lies than at detecting deception without lying, confirming a critical blind spot of current mechanistic deception detection approaches. It is proposed that future work should incorporate non-lying deception in dialogical settings into probe training and explore representations of second-order beliefs to more directly target the conceptual constituents of deception.

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