Xiaoyuan Wang
Author directory2026
Which Tokens Should SFT Actually Learn? A Token-Trimming Perspective on Mathematical Reasoning
Yaning Jia | Chunhui Zhang | Wenxuan Xu | Xingjian Diao | Xiaoyuan Wang | Soroush Vosoughi
Findings of the Association for Computational Linguistics: EMNLP 2026
Yaning Jia | Chunhui Zhang | Wenxuan Xu | Xingjian Diao | Xiaoyuan Wang | Soroush Vosoughi
Findings of the Association for Computational Linguistics: EMNLP 2026
Supervised fine-tuning (SFT) applies a uniform cross-entropy loss to all target tokens, even though different tokens provide unequal learning signals for mathematical reasoning. This uniform treatment can over-sharpen already mastered tokens while amplifying learning pressure on uncertain, low-confidence tokens, leading to suboptimal training dynamics. We propose Trimmed Logit-Gap SFT (TrimSFT), a simple token-level reweighting method that scales the SFT loss according to the logit gap between the gold token and its strongest competitor. TrimSFT trims supervision away from both extremes: tokens already mastered (large logit gap) and tokens weakly supported by the current model (small or negative logit gap), concentrating learning within an intermediate logit-gap region between them. We instantiate this principle with a Gaussian weight centered at margin m with bandwidth τ, requiring no reference model or additional forward pass. We evaluate TrimSFT on six base models from the Llama, Qwen, and DeepMath families across five mathematical reasoning benchmarks. TrimSFT consistently improves over standard SFT, achieving the best average performance on five out of six models, with gains of up to +26.9 points over SFT on MATH500. Further analyses show that the bandwidth τ matters more than the exact margin location, and that half-trim variants that remove supervision pressure from only one side yield inferior trade-offs. A token-level logit-gap distribution analysis suggests that TrimSFT reshapes model confidence in a more balanced way than uniform SFT or monotonic reweighting methods. These results suggest that reasoning SFT can benefit from trimming both extremes rather than treating all tokens uniformly.
Relevant Is Not Warranted: Evidence-Force Calibration for Cited RAG
Pin Qian | Su Wang | Yihang Chen | Wenxuan Xu | Xiaoyuan Wang | Qiaolin Yu | Shuhuai Lin | Sipeng Zhang | Junxian You | Xinpeng Wei
Findings of the Association for Computational Linguistics: EMNLP 2026
Pin Qian | Su Wang | Yihang Chen | Wenxuan Xu | Xiaoyuan Wang | Qiaolin Yu | Shuhuai Lin | Sipeng Zhang | Junxian You | Xinpeng Wei
Findings of the Association for Computational Linguistics: EMNLP 2026
Cited RAG evaluation often treats visible sources as a grounding signal, but a real, topically relevant citation can still under-warrant the attached wording. We study this diagnostic failure as citation laundering: a related source is presented as warrant for an over-strong claim. We introduce ForceBench, a contrastive stress test for evidence-force calibration. Each item holds a cited passage fixed and pairs an evidence-calibrated claim with a localized force-raised variant across five operational axes: relation, modality, scope, temporal validity, and numeric specificity. A calibrated evaluator should score the evidence-calibrated claim higher. Headline experiments use a fixed, locality-filtered 198-pair evaluation set. A citation-presence sanity check is uninformative by design; token and entity overlap still violate monotonicity on 32.8–36.4% of pairs. Across four reported model judges, standard generic support prompting is insufficient for this force-calibration stress test (aggregate MVR 47.2%), while explicit warrant-strength prompting lowers MVR to 24.5% but remains imperfect. We release the benchmark, prompts, outputs, and plug-in pipeline so citation evaluators can report monotonicity violation rate and force sensitivity alongside conventional support metrics.