arXiv AI By Chenlu Ding, Jiancan Wu, Yanchen Luo, Zheyuan Liu, Yancheng Yuan, Xiang Wang

Teaching Large Language Models When Not to Know: Learning Temporal Critique for Ex-Ante Reasoning

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The paper investigates how large language models (LLMs) incorrectly use post‑cutoff information when asked to answer from an earlier time, a problem termed temporal leakage. It shows that explicit cutoff statements and prefix constraints reduce leakage more effectively than implicit framing or suffix constraints, but that prompting alone cannot give models the ability to verify temporal admissibility. To overcome this, the authors introduce Temporal Critique Fine‑Tuning (TCFT), which trains models to detect and explain post‑cutoff leakage and judge whether a response is temporally admissible, achieving significant reductions in leakage on Qwen2.5 models.

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