ResearchResearch paperLarge Language Models · Interpretability1 source · Oct 14, 2026

Gray-Box Hallucination Detection in LLMs with Token Identities

We introduce GURI (Gray-box Uncertainty Representations with Identity), a lightweight gray-box hallucination detector that combines candidate-token probabilities with per-token vector identifiers.

Key points

  • Large language models often produce fluent but factually incorrect output.
  • Gray-box detectors identify such hallucinations from the token-probability statistics emitted during generation, avoiding the need for white-box access to hidden states that frontier models do not provide.
  • These detectors, however, typically rely only on probability-derived representations and ignore the identities of the candidate tokens.
  • For the three open-weight models, cross-dataset transfer between HotpotQA and TriviaQA with the model held fixed improves mean ROC-AUC over transferred LOS-Net by 3.76 points.

Sources (1)

  • [1]Gray-Box Hallucination Detection in LLMs with Token Identities
    arXiv (AI, ML, NLP, CV, robotics, multi-agent) · Oct 14, 11:12 AM
    We introduce GURI (Gray-box Uncertainty Representations with Identity), a lightweight gray-box hallucination detector that combines candidate-token probabilities with per-token vector identifiers.
    Large language models often produce fluent but factually incorrect output.

Extractive summary: sentences quoted from the sources.

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