From Harm to Help: Turning Reasoning In-Context Demos into Assets for Reasoning LMs

Weida Liang, Zihang Fu, Haonan Wang, Zheng Nie, Yifan Zhang, Yao Tong, Tongyao Zhu, Hao Jiang, Chuang Li, Jiaying Wu, Kenji Kawaguchi


Abstract
Recent reasoning LLMs (RLMs), especially those trained with verifier-based reinforcement learning, often perform worse with few-shot CoT than with direct answering. We revisit this paradox using high-quality reasoning traces from DeepSeek-R1 as demonstrations and find that adding more exemplars consistently degrades accuracy, even when demonstrations are optimal. A detailed analysis reveals two mechanisms behind this decline: (i) *semantic misguidance*, where high textual similarity leads the model to treat the target as the same as the exemplar and to copy intermediate steps verbatim; and (ii) *strategy transfer failure*, where the model struggles to extract useful reasoning strategies and apply them to target questions. Guided by these findings, we introduce Insight-to-Solve (I2S), which converts demonstrations into target-conditioned insights before solving, and I2S+, which adds iterative refinement. Across open- and closed-source models, both variants outperform direct answering and sequential test-time baselines. On a frozen 500-problem Omni-MATH transfer set, I2S+ improves R1-Distill-Qwen-7B and Qwen3-14B by +4.2 and +4.0 points, respectively. The same prompt stack also transfers to GPT-4.1, o1-mini, and R1-Distill-Llama-8B, showing that reasoning demonstrations can be converted from liabilities into useful test-time guidance.
Anthology ID:
2026.findings-emnlp.66
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
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SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
1333–1355
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URL:
https://aclanthology.org/2026.findings-emnlp.66/
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Cite (ACL):
Weida Liang, Zihang Fu, Haonan Wang, Zheng Nie, Yifan Zhang, Yao Tong, Tongyao Zhu, Hao Jiang, Chuang Li, Jiaying Wu, and Kenji Kawaguchi. 2026. From Harm to Help: Turning Reasoning In-Context Demos into Assets for Reasoning LMs. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 1333–1355, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
From Harm to Help: Turning Reasoning In-Context Demos into Assets for Reasoning LMs (Liang et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.66.pdf