Beyond Surface Statistics: Robust Conformal Prediction for LLMs via Internal Representations

• URL: http://arxiv.org/abs/2604.16217v1
• Date: Fri, 17 Apr 2026 16:28:31 GMT
• Title: Beyond Surface Statistics: Robust Conformal Prediction for LLMs via Internal Representations
• Abstract summary: We propose a conformal framework for question answering that uses internal representations rather than output-facing statistics.<n>We show that our method achieves a better validity--efficiency trade-off than strong text-level baselines.<n>These results suggest that internal representations can provide more informative conformal scores when surface-level uncertainty is unstable under distribution shift.
• Score: 36.24681446361556
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Large language models are increasingly deployed in settings where reliability matters, yet output-level uncertainty signals such as token probabilities, entropy, and self-consistency can become brittle under calibration--deployment mismatch. Conformal prediction provides finite-sample validity under exchangeability, but its practical usefulness depends on the quality of the nonconformity score. We propose a conformal framework for LLM question answering that uses internal representations rather than output-facing statistics: specifically, we introduce Layer-Wise Information (LI) scores, which measure how conditioning on the input reshapes predictive entropy across model depth, and use them as nonconformity scores within a standard split conformal pipeline. Across closed-ended and open-domain QA benchmarks, with the clearest gains under cross-domain shift, our method achieves a better validity--efficiency trade-off than strong text-level baselines while maintaining competitive in-domain reliability at the same nominal risk level. These results suggest that internal representations can provide more informative conformal scores when surface-level uncertainty is unstable under distribution shift.

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