Knowing Before Answering: Decoding Language Models for Reliable RAG

Researchers from an unnamed team have developed a feature-based router that uses language models' internal signals to classify whether retrieved documents in Retrieval-Augmented Generation (RAG) are sufficient, insufficient, or conflicting, outperforming prompting-based baselines across 16 language models. The study, posted on arXiv (2608.27661v1), shows that hidden activations, especially in middle layers, are the most informative for this three-way classification, enabling reliable RAG triage.

arXiv:2608.27661v1 Announce Type: new Abstract: In Retrieval-Augmented Generation RAG , retrieval may provide insufficient or conflicting information needed to answer a question. The system should not only know when to answer but also be able to identify cases in which the documents provided in RAG are insufficient or contain conflicting information. This can be framed as a three-way classification problem, where we use the model's internal signals to determine whether the provided information in the input can be classified as sufficient, insufficient, or conflicting. We create a controlled benchmark dataset that replicates a RAG setup with fictitious information and labels each instance as answerable, insufficient, or conflicting. We use hidden activations and attention-derived features as inputs to train a lightweight linear model to distinguish among the three classes. Across 16 language models spanning different architectures and a range of model sizes, our feature-based router consistently outperforms prompting-based baselines and the performance of specialised RAG-models. We further conduct analyses into the information dynamics of the models. We show that the most informative signals for the classification are available in the middle layers, with hidden activation states being more effective than attention values or the MLP-feature outputs in most of the tested models. Overall, our results suggest that language models internally encode whether retrieved evidence is sufficient to support answering, and that this signal can be decoded reliably for RAG triage.