Prediction of Prediction (PoP): Inter-Layer Activation Fusion for Single-Pass Hallucination Detection in Large Language Models

Abstract:Autoregressive large language models (LLMs) routinely generate factually incorrect outputs with high decoding confidence, limiting their deployment in high-stakes workflows. Existing output-stage uncertainty metrics can fail when models are overconfident on false assertions, while multi-sample verification pipelines introduce substantial memory and latency overhead. This work evaluates whether internal hidden-state transition dynamics during generation can signal factual errors without auxiliary decoding calls. We introduce Prediction of Prediction (PoP), a mechanism that captures layer-transition uncertainty by fusing intermediate hidden representations across depth during a single forward pass. Evaluated on the TruthfulQA benchmark using autoregressive transformer backbones, PoP achieves an area under the receiver operating characteristic curve (AUROC) of 75.5% for factual-correctness classification. The mechanism operates within the base forward pass, adding less than 1.2% runtime latency and requiring zero additional generation passes. The numerical results are reported from the author-verified experimental implementation and are bounded by the evaluation scope described below.

7 pages, 3 figures, 9 tables. Single-author preprint on white-box, single-pass hallucination detection using inter-layer activation divergence, cross-layer fusion, temporal drift, and calibrated risk scoring. Evaluated on TruthfulQA, HaluEval 2.0, and FaithDial with Llama-3, Qwen2.5, and Mistral backbones

Computation and Language (cs.CL)

arXiv:2608.27165 [cs.CL]

(or arXiv:2608.27165v1 [cs.CL] for this version)

https://doi.org/10.48550/arXiv.2608.27165 arXiv-issued DOI via DataCite (pending registration)