Rationale-Grounded In-Context Learning for Time Series Reasoning with Multimodal Large Language Models

Qingxiang Liu, Zhiqing Cui, Xiaoliang Luo, Yuqian Wu, Zhuoyang Jiang, Huaiyu Wan, Sheng Sun, Lvchun Wang, Wei Yu, Yuxuan Liang


Abstract
The underperformance of existing multimodal large language models for time series reasoning lies in the absence of rationale priors that connect temporal observations to their downstream outcomes, which leads models to rely on superficial pattern matching rather than principled reasoning. We therefore propose the rationale-grounded in-context learning for time series reasoning, where rationales work as guiding reasoning units rather than post-hoc explanations, and develop the RationaleTS method. Specifically, we firstly induce label-conditioned rationales, composed of reasoning paths from observable evidence to the potential outcomes. Then, we design the hybrid retrieval by balancing temporal patterns and semantic contexts to retrieve correlated rationale priors for the final in-context inference on new samples. We conduct extensive experiments to demonstrate the effectiveness and efficiency of our proposed RationaleTS on three-domain time series reasoning tasks. We provide the source code in https://github.com/yuppielqx/RationaleTS.
Anthology ID:
2026.findings-emnlp.1816
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:
38806–38824
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URL:
https://aclanthology.org/2026.findings-emnlp.1816/
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Cite (ACL):
Qingxiang Liu, Zhiqing Cui, Xiaoliang Luo, Yuqian Wu, Zhuoyang Jiang, Huaiyu Wan, Sheng Sun, Lvchun Wang, Wei Yu, and Yuxuan Liang. 2026. Rationale-Grounded In-Context Learning for Time Series Reasoning with Multimodal Large Language Models. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 38806–38824, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Rationale-Grounded In-Context Learning for Time Series Reasoning with Multimodal Large Language Models (Liu et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.1816.pdf