Pengcheng Wen
Author directory2026
Glance-or-Gaze: Incentivizing LMMs to Adaptively Focus Search via Reinforcement Learning
Hongbo Bai | Yujin Zhou | Yile Wu | Chi-Min Chan | Pengcheng Wen | Kunhao Pan | Sirui Han | Yike Guo
Findings of the Association for Computational Linguistics: ACL 2026
Hongbo Bai | Yujin Zhou | Yile Wu | Chi-Min Chan | Pengcheng Wen | Kunhao Pan | Sirui Han | Yike Guo
Findings of the Association for Computational Linguistics: ACL 2026
Large Multimodal Models (LMMs) have achieved remarkable success in visual understanding, yet they struggle with knowledge-intensive queries involving long-tail entities or evolving information due to static parametric knowledge. Recent search-augmented approaches attempt to address this limitation, but existing methods rely on indiscriminate whole-image retrieval that introduces substantial visual redundancy and noise, and lack deep iterative reflection, limiting their effectiveness on complex visual queries. To overcome these challenges, we propose Glance-or-Gaze (GoG), a fully autonomous framework that shifts from passive perception to active visual planning. GoG introduces a Selective Gaze mechanism that dynamically chooses whether to glance at global context or gaze into high-value regions, filtering irrelevant information before retrieval. We design a dual-stage training strategy: Reflective GoG Behavior Alignment via supervised fine-tuning instills the fundamental GoG paradigm, while Complexity-Adaptive Reinforcement Learning further enhances the model’s capability to handle complex queries through iterative reasoning. Experiments across six benchmarks demonstrate state-of-the-art performance. Ablation studies confirm that both Selective Gaze and complexity-aware RL are essential for effective visual search. We will release our data and models for further exploration soon.
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.
Omni-RewardBench: Toward a Comprehensive Evaluation of Generative Reward Models Across Modalities
Chi-Min Chan | Yujin Zhou | Pengcheng Wen | Boqin Yin | 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 | Yujin Zhou | Pengcheng Wen | Boqin Yin | 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)
The rise of Omni-modality Large Language Models (OLLMs) capable of jointly processing text, audio, and visual inputs marks a major step toward general intelligence. Ensuring their alignment with human preferences requires effective Omni-modality Reward Models (ORMs), which serve as surrogates for human judgment to guide OLLMs behavior. However, ORMs evaluation remains underdeveloped in the previous literature. Existing benchmarks are largely text-centric or limited to bimodal tasks, restricting comprehensive assessment for ORMs. To bridge this gap, we introduce Omni-RewardBench, the first benchmark for comprehensive evaluation of ORMs across modalities. In short, our contributions are threefold: (1) a hybrid automatic-annotation and human-verification pipeline to construct high-quality evaluation data; (2) extensive experiments on 20+ models, including inherently omni-modal and modality-bridged systems. Our experimental results demonstrate that current OLLMs fall short as reward models, revealing several common failure modes such as perception failure, modality dominance failure, and cross-modal fusion failure; and (3) strong correlations between Omni-RewardBench scores and downstream performance (IID r = 0.94, OOD r = 0.72), validating its reliability as a predictor of real-world capability and alignment quality.
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
Boosting Policy and Process Reward Models with Monte Carlo Tree Search in Open-Domain QA
Chi-Min Chan | Chunpu Xu | Junqi Zhu | Jiaming Ji | Donghai Hong | Pengcheng Wen | Chunyang Jiang | Zhen Ye | Yaodong Yang | Wei Xue | Sirui Han | Yike Guo
Findings of the Association for Computational Linguistics: ACL 2025
Chi-Min Chan | Chunpu Xu | Junqi Zhu | Jiaming Ji | Donghai Hong | Pengcheng Wen | Chunyang Jiang | Zhen Ye | Yaodong Yang | Wei Xue | Sirui Han | Yike Guo
Findings of the Association for Computational Linguistics: ACL 2025
The recent introduction of OpenAI’s O1/O3 model represents a significant milestone in developing strong reasoning capabilities in Large Language Models (LLMs). By introducing more computational budget during test-time, LLMs have the potential to explore more accurate and higher-quality solutions. However, such paradigms are primarily verified in domains that have well-defined criteria for responses, such as coding and mathematics. Inspired by the success of this paradigm, we aim to bridge it to more subtle open-domain question answering. Specifically, we utilize search mechanisms such as Monte Carlo Tree Search (MCTS) for both policy model improvement and reward model improvement that achieve better performance in test-time scaling strategies. Our contributions are summarized in two folds: For the training phase, we demonstrate that our approach surpasses previous SOTA automatic data annotation methods and various public instruction-tuning datasets, with fewer data points. This offers a more data-efficient solution for training robust models. For the inference phase, we utilize the intermediate values collected during training data construction to train a process reward model called PRM+. This model employs a novel two-stage training method to provide finer-grained guidance across the generation trajectory. This introduces no additional overhead during training data collection and further enhances performance by scaling test-time computation. Experimental results show that our method can effectively improve the performance of both the policy model and the reward model.