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arXiv · 2606.23048

HALAS: A Human-Annotated Dataset of Hallucinations of Modern ASR Systems

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

End-to-end Automatic Speech Recognition (ASR) systems hallucinate on natural speech, yet existing mitigation methods are typically evaluated on non-speech or artificially corrupted audio. We introduce HALAS, the first human-annotated dataset of naturally occurring hallucinations from seven state-of-the-art ASR models on real unprocessed earnings call recordings. HALAS provides span-level labels, enabling analysis of hallucination patterns and their severity. Our analysis reveals strong cross-model vocabulary overlap and confirms that hallucinations also occur for almost correctly transcribed speech (characterized by a low Word Error Rate). The proposed benchmark with HALAS shows that the character and semantic-level metrics used as a proxy for hallucination detection reach 81% ROC-AUC, while state-of-the-art detection methods achieve an F1 score of only 53.1%. As such, HALAS establishes the first rigorous non-artificial benchmark for the detection and mitigation of ASR hallucinations.

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Mateusz Barański, Jan Jasiński, Julitta Bartolewska, Marcin Witkowski, Konrad Kowalczyk. 2026-06-22. HALAS: A Human-Annotated Dataset of Hallucinations of Modern ASR Systems. https://arxiv.org/abs/2606.23048

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