Streaming Hallucination Detection in Long Chain-of-Thought Reasoning

Haolang Lu, Minghui Pan, Ripeng LI, Guoshun Nan, Jialin Zhuang, Zijie Zhao, Zhongxiang Sun, Kun Wang, Yang Liu


Abstract
Long chain-of-thought (CoT) reasoning improves the performance of large language models, yet hallucinations in such settings often emerge subtly and propagate across reasoning steps. We suggest that hallucination in long CoT reasoning is better understood as an evolving latent state rather than a one-off erroneous event. Accordingly, we treat step-level hallucination judgments as local observations and introduce a cumulative prefix-level hallucination signal that tracks the global evolution of the reasoning state over the entire trajectory. Overall, our approach enables streaming hallucination detection in long CoT reasoning, providing real-time, interpretable evidence.
Anthology ID:
2026.findings-acl.1064
Volume:
Findings of the Association for Computational Linguistics: ACL 2026
Month:
July
Year:
2026
Address:
San Diego, California, United States
Editors:
Maria Liakata, Viviane P. Moreira, Jiajun Zhang, David Jurgens
Venue:
Findings
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Publisher:
Association for Computational Linguistics
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Pages:
21157–21183
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URL:
https://preview.aclanthology.org/ingest-acl/2026.findings-acl.1064/
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Cite (ACL):
Haolang Lu, Minghui Pan, Ripeng LI, Guoshun Nan, Jialin Zhuang, Zijie Zhao, Zhongxiang Sun, Kun Wang, and Yang Liu. 2026. Streaming Hallucination Detection in Long Chain-of-Thought Reasoning. In Findings of the Association for Computational Linguistics: ACL 2026, pages 21157–21183, San Diego, California, United States. Association for Computational Linguistics.
Cite (Informal):
Streaming Hallucination Detection in Long Chain-of-Thought Reasoning (Lu et al., Findings 2026)
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https://preview.aclanthology.org/ingest-acl/2026.findings-acl.1064.pdf
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