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arXiv · 2606.23060

From Text Metrics to Model Internals: A Study of Whisper ASR Hallucination Detection

Jan Jasiński·Mateusz Barański·Julitta Bartolewska·Marcin Witkowski·Konrad Kowalczyk
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Abstract

Hallucinations of ASR models - fluent transcriptions with no basis in audio - degrade system performance and pose risks in downstream applications. Robust detection of such errors remains a challenge. This paper studies Whisper large v3 hallucination detection on real-speech human-annotated data across three paradigms: text-based, LLM-based, and internal decoder state probing. Text classifiers utilizing metrics for text evaluation achieve high recall but degrade without reference transcripts. LLM-based detection improves precision with domain-specific prompt conditioning, yet remains less competitive than the lightweight text-based methods. Probing Whisper's decoder representations, without a ground-truth reference, yields the strongest performance, revealing that hallucination traits are encoded across intermediate decoding layers. A late-fusion meta-classifier combining text and internal-state outputs achieves the best overall detection performance.

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Jan Jasiński, Mateusz Barański, Julitta Bartolewska, Marcin Witkowski, Konrad Kowalczyk. 2026-06-22. From Text Metrics to Model Internals: A Study of Whisper ASR Hallucination Detection. https://arxiv.org/abs/2606.23060

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