arXiv Computation and Language By Alexandra Kuleshova, Andrey Volodichev, Daria Kotova, Alexey Zaytsev

What LLMs Do in the Shadows: Reading Context Reliance from the Unembedding Dark Space

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The paper introduces DarkLens, a lightweight method for detecting faithfulness hallucinations in large language models (LLMs). It estimates context reliance by projecting hidden states onto the dark space—directions weakly aligned with the unembedding matrix—and uses the resulting Dark Matter Ratio (DMR) as a direct score of context utilization. Combined with a parametric knowledge score, DarkLens operates within a single forward pass and outperforms many baselines on QA and summarization benchmarks across several open‑weight LLMs.

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