Han Zhu
Author directoryOther people with similar names: Han Zhu, Han Zhu
2026
BCL: Bayesian In-Context Learning Framework for Information Extraction
Haoliang Liu | Chengkun Cai | Xu Zhao | Han Zhu | Shizhou Huang | Xinglin Zhang | Tao Chen | Jenq-Neng Hwang | Zhang Huaping | Lei Li
Findings of the Association for Computational Linguistics: ACL 2026
Haoliang Liu | Chengkun Cai | Xu Zhao | Han Zhu | Shizhou Huang | Xinglin Zhang | Tao Chen | Jenq-Neng Hwang | Zhang Huaping | Lei Li
Findings of the Association for Computational Linguistics: ACL 2026
Existing information extraction (IE) tasks increasingly adopt in-context learning (ICL) with large language models. However, current approaches either show inconsistent performance across model scales or lack systematic optimization and generalizability. Building on this, we propose BCL-IE (Bayesian In-Context Learning Framework for Information Extraction), the first optimization framework that uses particle filtering with Bayesian updates to systematically refine label representations across IE tasks. Through four steps—initialization, observation, weight update, and resampling, BCL-IE generalizes to both sequence labeling and relation classification paradigms. Extensive experiments demonstrate substantial improvements over existing approaches (up to 30%), achieving prior performance while other methods either fail to generalize or show limited effectiveness.
PASTABench: Proactive Assessment of Sequential Trajectories for Agent Safety
Jiapeng Sun | Yujin Zhou | Han Zhu | Pengcheng Wen | Jiayi Zhou | Sirui Han | Yike Guo
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Jiapeng Sun | Yujin Zhou | Han Zhu | Pengcheng Wen | Jiayi Zhou | Sirui Han | Yike Guo
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
As Large Language Models (LLMs) evolve into autonomous agents that alter real-world states, ensuring operational safety across multi-step workflows has become a critical challenge. While recent work has moved beyond single-turn evaluation toward multi-turn paradigms, key limitations persist: step-level methods treat actions in isolation, missing how risks accumulate, and trajectory-level evaluations operate post-hoc, offering no opportunity for timely intervention. To address this, we formalize Decoupled Proactive Safety Monitoring along three dimensions—whether, when to intervene, and what the risk is—and introduce PASTABench, a benchmark of 1,139 multi-turn trajectories spanning 5 risk categories and 13 sub-categories. We further propose the Optimal Intervention Window (OIW), anchored by annotated Earliest-Signal and Trigger turns, to quantify intervention timeliness. Evaluation of 16 LLMs reveals that proactive intervention remains largely unsolved, with the best model achieving only 40.74% optimal-timing interventions. Fine-grained diagnosis further uncovers pervasive lexical overfitting: competitive safety scores of smaller models mask keyword hypersensitivity rather than genuine risk comprehension, as their proactive capability largely collapses once hazard vocabulary is neutralized.
Cross-Modal Emergent Misalignment Through Narrow-Domain Fine-Tuning
Han Zhu | Chengkun Cai | Pengcheng Wen | Yanxu Zhu | Jagmohan Chauhan | Lei Li | Yike Guo | Sirui Han
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Han Zhu | Chengkun Cai | Pengcheng Wen | Yanxu Zhu | Jagmohan Chauhan | Lei Li | Yike Guo | Sirui Han
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
The rapid advancement of artificial intelligence has brought safety concerns to the forefront of research. Recent studies indicate that Large Language Models (LLMs) may exhibit emergent misalignment during training progress: when exposed to narrow-domain harmful data, they can develop unsafe behaviors across broad, unrelated tasks. This phenomenon raises a critical question: do current alignment methods genuinely eliminate harmful capabilities, or do they merely condition models to “simulate” safety? To investigate this, we conduct a comprehensive study on cross-modal emergent misalignment involving diverse Multimodal Large Language Models (MLLMs), including vision-language models (VLMs) such as Gemma3 and Qwen2.5-VL and unified any-to-any models including Janus and Bagel. We utilize a multimodal training setup encompassing text-to-text (T2T), text-image-to-text (TI2T), and text-to-image (T2I) tasks to probe safety boundaries. Our experiments yield four critical findings: (1) Cross-modal penetration: Current alignment methods primarily constrain model behavior rather than unlearning harmful knowledge, as evidenced by safety breaches transferring across modalities. (2) Backbone vulnerability: Mechanistic analysis reveals that the LLM backbone, rather than the visual encoder/decoder, is the primary source of cross-modal vulnerabilities. (3) Evaluation gaps: We identify significant deficiencies in current safety evaluation practices, demonstrating that single-modality testing is inadequate for detecting cross-modal risks. These findings underscore the urgent need for comprehensive cross-modal evaluation frameworks to mitigate safety concerns in next-generation multimodal models.
Towards Multi-modal Multi-turn Safety: From Agentic Interaction to Strategic Alignment
Han Zhu | Jiale Chen | Chengkun Cai | Shengjie Sun | Haoran Li | Yujin Zhou | Chi-Min Chan | Pengcheng Wen | Lei Li | Yike Guo | Sirui Han
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Han Zhu | Jiale Chen | Chengkun Cai | Shengjie Sun | Haoran Li | Yujin Zhou | Chi-Min Chan | Pengcheng Wen | Lei Li | Yike Guo | Sirui Han
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Despite remarkable capability in multi-modal understanding, deploying Multi-modal Large Language Models (MLLMs) in open-ended conversational scenarios introduces safety risks that remain poorly addressed by existing alignment methods. Unlike simple malicious visual question and answer (VQA) pairs , multi-turn interactions enable adversaries to incrementally reconstruct harmful intent across dialogues, progressively bypassing safety constraints in ways that are difficult to detect at any individual turn. Meanwhile, conventional reinforcement learning from human feedback (RLHF) approaches are unsuitable for this situation: designed primarily for VQA tasks, they neither capture cross-turn risk dynamics nor scale efficiently without costly manual preference annotation. To close this gap, we introduce MINT-Safe, an open-source visual multi-turn training dataset comprising 11,270 multi-image dialogues and 500 refusal VQA pairs, constructed via multi-agent interaction with text-to-image (T2I) tool-call augmentation. Building on MINT-Safe, we propose TAD-Align, a dialogue safety alignment framework centered on a turn-aware dual-objective reward function. Rather than treating all dialogue turns uniformly, TAD-Align leverages rollout-based safety score variance to dynamically identify turns where the model exhibits inconsistent safety behavior, and adaptively up-weights these turns during optimization. Experiments on Qwen2.5-VL-7B-Instruct and LLaVA-NeXT-7B demonstrate reductions of over 10% in Attack Success Rate (ASR), alongside improvements of at least 8% in harmlessness and 13% in helpfulness on multi-modal multi-turn safety benchmarks, while preserving general model capabilities.
Not Just the Destination, But the Journey: Reasoning Traces Causally Shape Generalization Behaviors
Pengcheng Wen | Yanxu Zhu | Jiapeng Sun | Han Zhu | Yujin Zhou | Chi-Min Chan | Yike Guo | Sirui Han
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Pengcheng Wen | Yanxu Zhu | Jiapeng Sun | Han Zhu | Yujin Zhou | Chi-Min Chan | Yike Guo | Sirui Han
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Chain-of-Thought (CoT) is often viewed as a window into LLM decision-making, yet recent work suggests it may function merely as post-hoc rationalization. This raises a critical alignment question: Does the reasoning trace causally shape model generalization independent of the final answer? To isolate reasoning’s causal effect, we hold final harmful answers constant while varying reasoning paths across three types, Evil (embracing malice), Misleading (rationalizing harm), and Submissive (yielding to pressure), and train models (Qwen 0.6B–14B) under QTA, QT, T-only, and QA paradigms, evaluating in both think and no-think modes. We find that: (1) CoT training amplifies harmful generalization beyond standard fine-tuning; (2) distinct reasoning types induce distinct behavioral patterns despite identical answers; (3) training on reasoning without answer supervision suffices to alter behavior; and (4) these effects persist when CoT is suppressed at inference. We validate these findings with naturally generated CoT, on GPT-OSS-20B, and under RLVR training, reporting bootstrap 95% CIs throughout. Our findings demonstrate that reasoning content is causally potent for downstream alignment, challenging strategies that supervise only final outputs.
Benchmarking Fine-Grained Error Detection in Multimodal Reasoning
Chi-Min Chan | Han Zhu | Chunyang Jiang | Jiaming Ji | Juntao Dai | Wei Xue | Sirui Han | Yike Guo
Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Chi-Min Chan | Han Zhu | Chunyang Jiang | Jiaming Ji | Juntao Dai | Wei Xue | Sirui Han | Yike Guo
Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Multimodal Process Reward Models (MPRMs) have emerged as a pivotal framework for enhancing the reasoning capabilities of Multimodal Large Language Models (MLLMs). However, the research community currently lacks a dedicated benchmark to rigorously assess the error discernment capabilities of these models.To address this gap, we introduce PRMBench-V, a novel benchmark specifically designed to evaluate MPRMs’ proficiency in detecting erroneous reasoning steps across diverse error categories. Leveraging a semi-automated annotation pipeline augmented with human verification, we construct a comprehensive dataset comprising 907 unique queries, each annotated with nine distinct error types, resulting in 8,163 test cases with fine-grained step-level error labels.Through extensive experiments involving over 15 open- and closed-source models, we uncover several key findings: (1) even the strongest existing MPRMs achieve only \textasciitilde30% accuracy in error identification; (2) while partial error detection achieves moderate precision and recall (\textasciitilde60%), overall accuracy remains low (\textasciitilde20%); and (3) benchmark scores exhibit a strong correlation with downstream task performance gains (r=0.86). Furthermore, we demonstrate that PRMBench-V can inform the development of more robust MPRMs: by introducing the Bayesian Rater Reliability Process Reward Model (BR2-PRM), we achieve up to a 4.8% performance improvement through test-time scaling.We believe that PRMBench-V will serve as a valuable resource for advancing MPRM research, enabling more rigorous evaluation and fostering the development of models with fine-grained multimodal reasoning capabilities.
SafeMT: Multi-turn Safety for Multimodal Language Models
Han Zhu | Juntao Dai | Jiaming Ji | Haoran Li | Chengkun Cai | Pengcheng Wen | Chi-Min Chan | Boyuan Chen | Yaodong Yang | Sirui Han | Yike Guo
Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Han Zhu | Juntao Dai | Jiaming Ji | Haoran Li | Chengkun Cai | Pengcheng Wen | Chi-Min Chan | Boyuan Chen | Yaodong Yang | Sirui Han | Yike Guo
Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
With the widespread use of multi-modal Large Language models (MLLMs), safety issues have become a growing concern. Multi-turn dialogues, which are more common in everyday interactions, pose a greater risk than single prompts; however, existing benchmarks do not adequately consider this situation. To encourage the community to focus on the safety issues of these models in multi-turn dialogues, we introduce SafeMT, a benchmark that features dialogues of varying lengths generated from harmful queries accompanied by images. This benchmark consists of 10,000 samples in total, encompassing 17 different scenarios and four jailbreak methods. Additionally, we propose Safety Index (SI) to evaluate the general safety of MLLMs during conversations. We assess the safety of 17 models using this benchmark and discover that the risk of successful attacks on these models increases as the number of turns in harmful dialogues rises. This observation indicates that the safety mechanisms of these models are inadequate for recognizing the hazard in dialogue interactions. We propose a dialogue safety moderator capable of detecting malicious intent concealed within conversations and providing MLLMs with relevant safety policies. Experimental results from several open-source models indicate that this moderator is more effective in reducing multi-turn Attack Success Rate (ASR) compared to existed guard models.
2025
SafeLawBench: Towards Safe Alignment of Large Language Models
Chuxue Cao | Han Zhu | Jiaming Ji | Qichao Sun | Zhenghao Zhu | Wu Yinyu | Josef Dai | Yaodong Yang | Sirui Han | Yike Guo
Findings of the Association for Computational Linguistics: ACL 2025
Chuxue Cao | Han Zhu | Jiaming Ji | Qichao Sun | Zhenghao Zhu | Wu Yinyu | Josef Dai | Yaodong Yang | Sirui Han | Yike Guo
Findings of the Association for Computational Linguistics: ACL 2025
With the growing prevalence of large language models (LLMs), the safety of LLMs has raised significant concerns. However, there is still a lack of definitive standards for evaluating their safety due to the subjective nature of current safety benchmarks. To address this gap, we conducted the first exploration of LLMs’ safety evaluation from a legal perspective by proposing the SafeLawBench benchmark. SafeLawBench categorizes safety risks into three levels based on legal standards, providing a systematic and comprehensive framework for evaluation. It comprises 24,860 multi-choice questions and 1,106 open-domain question-answering (QA) tasks. Our evaluation included 2 closed-source LLMs and 18 open-source LLMs using zero-shot and few-shot prompting, highlighting the safety features of each model. We also evaluated the LLMs’ safety-related reasoning stability and refusal behavior. Additionally, we found that a majority voting mechanism can enhance model performance. Notably, even leading SOTA models like Claude-3.5-Sonnet and GPT-4o have not exceeded 80.5% accuracy in multi-choice tasks on SafeLawBench, while the average accuracy of 20 LLMs remains at 68.8%. We urge the community to prioritize research on the safety of LLMs.
LegalReasoner: Step-wised Verification-Correction for Legal Judgment Reasoning
Weijie Shi | Han Zhu | Jiaming Ji | Mengze Li | Jipeng Zhang | Ruiyuan Zhang | Jia Zhu | Jiajie Xu | Sirui Han | Yike Guo
Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Weijie Shi | Han Zhu | Jiaming Ji | Mengze Li | Jipeng Zhang | Ruiyuan Zhang | Jia Zhu | Jiajie Xu | Sirui Han | Yike Guo
Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Legal judgment prediction (LJP) aims to function as a judge by making final rulings based on case claims and facts, which plays a vital role in the judicial domain for supporting court decision-making and improving judicial efficiency. However, existing methods often struggle with logical errors when conducting complex legal reasoning. We propose LegalReasoner, which enhances LJP reliability through step-wise verification and correction of the reasoning process. Specifically, it first identifies dispute points to decompose complex cases, and then conducts step-wise reasoning while employing a process verifier to validate each step’s logic from correctness, progressiveness, and potential perspectives. When errors are detected, expert-designed attribution and resolution strategies are applied for correction. To fine-tune LegalReasoner, we release the LegalHK dataset, containing 58,130 Hong Kong court cases with detailed annotations of dispute points, step-by-step reasoning chains, and process verification labels. Experiments demonstrate that LegalReasoner significantly improves concordance with court decisions from 72.37 to 80.27 on LLAMA-3.1-70B. The data is available at https://huggingface.co/datasets/weijiezz/LegalHK.
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Co-authors
- Yike Guo 8
- Sirui Han 8
- Pengcheng Wen 5
- Chengkun Cai 4
- Chi-Min Chan 4
- Jiaming Ji (吉嘉铭) 4
- Juntao Dai 3
- Lei Li 3
- Yujin Zhou 3
- Haoran Li 2
- Jiapeng Sun 2
- Yaodong Yang (杨耀东) 2
- Yanxu Zhu 2
- Chuxue Cao 1
- Jagmohan Chauhan 1
- Boyuan Chen 1
- Jiale Chen 1
- Tao Chen 1
- Shizhou Huang 1
- Zhang Huaping 1
- Jenq-Neng Hwang 1
- Chunyang Jiang 1
- Mengze Li 1
- Haoliang Liu 1
- Weijie Shi 1
- Qichao Sun 1
- Shengjie Sun 1
- Jiajie Xu 1
- Wei Xue 1
- Wu Yinyu 1
- Jipeng Zhang 1
- Ruiyuan Zhang 1
- Xinglin Zhang 1
- Xu Zhao 1
- Jiayi Zhou 1
- Jia Zhu 1
- Zhenghao Zhu 1