China

Direct Preference Optimization (DPO) is a widely used offline preference optimization algorithm that enhances the simplicity and training stability of reinforcement learning through reward function reparameterization from PPO. Recently, SimPO (Simple Preference Optimization) and CPO (Contrastive Preference Optimization) have proposed reference-free preference optimization methods to simplify DPO&#39;s training process. We observe that these reference-free methods exhibit higher training efficiency but are prone to overoptimization, leading to performance degradation. To address these issues, we propose Self Preference Optimization (SPO). SPO employs the SiLU function to replace the conventional logsigmoid loss function. The SiLU function attains its minimum at a finite value, preventing the model from excessively amplifying the chosen-rejected sample probability ratio and thereby mitigating overoptimization problem. We theoretically demonstrate that the SPO loss is an upper bound of the DPO loss, implying that optimizing the SPO objective implicitly optimizes the DPO objective. We evaluate SPO&#39;s effectiveness across multiple benchmarks including AlpacaEval 2 and MT-Bench. Experimental results show that SPO achieves a 7% improvement over SimPO in length-controlled win rate on AlpacaEval 2, while demonstrating superior performance on MT-Bench.

EMNLP 2025

SPO: Self Preference Optimization with Self Regularization

preference optimization

machine learning for nlp

language modeling

## Welcome to EMNLP 2024! 
We are excited to welcome you to one of the most prominent conferences in the field of Natural Language Processing. This year, EMNLP 2024 is being held in a hybrid format,
offering both virtual and in-person participation in beautiful Miami. Due to a record-breaking number of submissions, we've expanded the total number of accepted papers to accommodate more cutting-edge research from around the globe.
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EMNLP 2024

EMNLP 2024 will take place in Miami, Florida from Nov 12th to Nov 16th, 2024, at the Hyatt Regency Miami Hote and on Underline for remote participants.

Direct Preference Optimization (DPO) is a widely used offline preference optimization algorithm that enhances the simplicity and training stability of reinforcement learning through reward function reparameterization from PPO. Recently, SimPO (Simple Preference Optimization) and CPO (Contrastive Preference Optimization) have proposed reference-free preference optimization methods to simplify DPO's training process. We observe that these reference-free methods exhibit higher training efficiency but are prone to overoptimization, leading to performance degradation. To address these issues, we propose Self Preference Optimization (SPO). SPO employs the SiLU function to replace the conventional logsigmoid loss function. The SiLU function attains its minimum at a finite value, preventing the model from excessively amplifying the chosen-rejected sample probability ratio and thereby mitigating overoptimization problem. We theoretically demonstrate that the SPO loss is an upper bound of the DPO loss, implying that optimizing the SPO objective implicitly optimizes the DPO objective. We evaluate SPO's effectiveness across multiple benchmarks including AlpacaEval 2 and MT-Bench. Experimental results show that SPO achieves a 7% improvement over SimPO in length-controlled win rate on AlpacaEval 2, while demonstrating superior performance on MT-Bench.

poster

## Welcome!
"I am excited to welcome you to this year’s edition of the Conference on Empirical Methods in Natural Language Processing! Importantly, it marks the 30th edition of EMNLP. With over 8,000 submissions, more than 3,000 accepted papers, and thousands of attendees, we have come a long way from that first
workshop, which had 14 accepted papers. As the field looks ahead, Suzhou is the fitting location for celebrating this milestone: rooted in a long literary tradition, yet modern and forward-looking, and home to a large share of the NLP community." 

*Message from the General Chair, Dirk Hovy*

Celebrate 30 Years of EMNLP! 
EMNLP 2025 will be held in Suzhou, China from November 5th to November 9th, 2025.

Large language models (LLMs) enhance security through alignment when widely used, but remain susceptible to jailbreak attacks capable of producing inappropriate content. Jailbreak detection methods show promise in mitigating jailbreak attacks through the assistance of other models or multiple model inferences. However, existing methods entail significant computational costs. In this paper, we first present a finding that the difference in output distributions between jailbreak and benign prompts can be employed for detecting jailbreak prompts. Based on this finding, we propose a Free Jailbreak Detection (FJD) method which prepends an affirmative instruction to the input and scales the logits by temperature to distinguish between jailbreak and benign prompts through the confidence of the first token. Furthermore, we enhance the detection performance of FJD through the integration of virtual instruction learning. Extensive experiments on aligned LLMs show that our FJD can effectively detect jailbreak prompts with almost no additional computational costs during LLM inference.

LLM Jailbreak Detection for (Almost) Free!

Large language models(LLMs) based Agents are increasingly pivotal in simulating and understanding complex human systems and interactions. We proposed the AI-Agent School (AAS) system, built around a self-evolving mechanism that leverages agents for simulating complex educational dynamics. Addressing the fragmented issues in teaching process modeling and the limitations of agents performance in simulating diverse educational participants, AAS constructs the Zero-Exp strategy, employs a continuous "experience-reflection-optimization" cycle, grounded in a dual memory base comprising experience and knowledge bases and incorporating short-term and long-term memory components. Through this mechanism, agents autonomously evolve via situated interactions within diverse simulated school scenarios. This evolution enables agents to more accurately model the nuanced, multi-faceted teacher-student engagements and underlying learning processes found in physical schools. Experiment confirms that AAS can effectively simulate intricate educational dynamics and is effective in fostering advanced agent cognitive abilities, providing a foundational stepping stone from the "Era of Experience" to the "Era of Simulation" by generating high-fidelity behavioral and interaction data.

Evolution in Simulation: AI-Agent School with Dual Memory for High-Fidelity Educational Dynamics

With the widespread applications of large language models (LLMs), aligning LLMs with human values has emerged as a critical challenge. For alignment, we always expect LLMs to be honest, positive, harmless, etc. And LLMs appear to be capable of generating the desired outputs after the alignment tuning process, such as the preference tuning via reinforcement learning from human feedback (RLHF). However, it also raises a question about **after alignment, do LLMs genuinely obtain a value distinction between positives and negatives, beyond the generation of positive outputs?** In this work, we start by investigating this question from the token distribution perspective. Our findings reveal that compared to the unaligned versions, LLMs after alignment exhibit a larger logits gap between positive and negative tokens at each generation step, which suggests that LLMs do obtain a value distinction of positives and negatives after alignment. Meanwhile, it also motivates us to achieve alignment by directly constructing such value distinction, thus alleviating the excessive reliance on computational resources required by training-time alignment. Specifically, we propose a representation editing method that intervenes the last hidden representation by amplifying the logits difference between positive and negative tokens (defined as anchor words). Experimental results demonstrate that the proposed method not only achieves effective alignment, but also requires fewer computational resources compared to training-time alignment methods

Constructing Your Model’s Value Distinction: Towards LLM Alignment with Anchor Words Tuning

Large Language Models have achieved significant advancements in various natural language processing tasks. However, they are susceptible to generating hallucinations-fabricated or inaccurate statements presented as factual information-which can undermine their reliability in high-stakes applications. To address this issue, we propose a new inference-stage hallucination mitigation method, Regularized Contrastive Decoding (RCD), to exploit hard negative samples for improving the robustness of contrastive decoding. Additionally, we design a new adversarial-aware regularization term to finetune hallucination models to learn more challenging and diverse hallucination patterns from available data with the guidance of adversarial perturbations. This enhances the contrastive decoding process, enabling more effective identification and filtering of erroneous content. We conduct experiments on four public hallucination benchmarks. Experimental results show our method achieves better hallucination mitigation performance consistently, proving the effectiveness and superiority of RCD for hallucination mitigation.

Regularized Contrastive Decoding with Hard Negative Samples for LLM Hallucination Mitigation

Refusal is a key safety behavior in aligned language models, yet the internal mechanisms driving refusals remain opaque. In this work, we conduct a mechanistic study of refusal in instruction-tuned LLMs using sparse autoencoders to identify latent features that causally mediate refusal behaviors. We apply our method to two open-source chat models and intervene on refusal-related features to assess their influence on generation, validating their behavioral impact across multiple harmful datasets. This enables a fine-grained inspection of how refusal manifests at the activation level and addresses key research questions such as investigating upstream-downstream latent relationship and understanding the mechanisms of adversarial jailbreaking techniques. We also establish the usefulness of refusal features in enhancing generalization for linear probes to out-of-distribution adversarial samples in classification tasks.

Understanding Refusal in Language Models with Sparse Autoencoders

As the use of large language model (LLM) agents continues to grow, their safety vulnerabilities have become increasingly evident. Extensive benchmarks evaluate various aspects of LLM safety by defining the safety relying heavily on general standards, overlooking user-specific standards. However, safety standards for LLM may vary based on a user-specific profiles rather than being universally consistent across all users. This raises a critical research question: Do LLM agents act safely when considering user-specific safety standards? Despite its importance for safe LLM use, no benchmark datasets currently exist to evaluate the user-specific safety of LLMs. To address this gap, we introduce U-SafeBench, a benchmark designed to assess user-specific aspect of LLM safety. Our evaluation of 20 widely used LLMs reveals current LLMs fail to act safely when considering user-specific safety standards, marking a new discovery in this field. To address this vulnerability, we propose a simple remedy based on chain-of-thought, demonstrating its effectiveness in improving user-specific safety.

Is Safety Standard Same for Everyone? User-Specific Safety Evaluation of Large Language Models

Safety-aligned LLMs respond to prompts with either compliance or refusal, each corresponding to distinct directions in the model’s activation space. Recent works show that initializing attacks via self-transfer from other prompts significantly enhances their performance. However, the underlying mechanisms of these initializations remain unclear, and attacks utilize arbitrary or hand-picked initializations. This work presents that each gradient-based jailbreak attack and subsequent initialization gradually converge to a single compliance direction that suppresses refusal, thereby enabling an efficient transition from refusal to compliance. Based on this insight, we propose CRI, an initialization framework that aims to project unseen prompts further along compliance directions. We demonstrate our approach on multiple attacks, models, and datasets, achieving an increased attack success rate (ASR) and reduced computational overhead, highlighting the fragility of safety-aligned LLMs. A reference implementation is available at https://anonymous.4open.science/r/CRI_for_paper-7BB5.

Jailbreak Attack Initializations as Extractors of Compliance Directions

The use of large language models (LLMs) as judges, particularly in preference comparisons, has become widespread, but this reveals a notable bias towards longer responses, undermining the reliability of such evaluations. To better understand such bias, we propose to decompose the preference evaluation metric, specifically the win rate, into two key components: desirability and information mass, where the former is length-independent and related to trustworthiness such as correctness, toxicity, and consistency, and the latter is length-dependent and represents the amount of information in the response. We empirically demonstrated the decomposition through controlled experiments and found that response length impacts evaluations by influencing information mass. To derive a reliable evaluation metric that assesses content quality without being confounded by response length, we propose AdapAlpaca, a simple yet effective adjustment to win rate measurement. Specifically, AdapAlpaca ensures a fair comparison of response quality by aligning the lengths of reference and test model responses under equivalent length intervals.

Explaining Length Bias in LLM-Based Preference Evaluations

Large language models (LLMs) exhibit exceptional capabilities across various tasks but also pose risks by generating harmful content. Existing safety mechanisms, while improving model safety, often lead to overly cautious behavior and fail to fully leverage LLMs’ internal cognitive processes. Inspired by humans' reflective thinking capability, we first show that LLMs can similarly perform internal assessments about safety in their internal states. Building on this insight, we propose **SafeSwitch**, a dynamic framework that regulates unsafe outputs by utilizing the prober-based internal state monitor that actively detects harmful intentions, and activates a safety head that leads to safer and more conservative responses only when necessary. SafeSwitch reduces harmful outputs by approximately 80% on harmful queries while maintaining strong utility, reaching a Pareto optimal among several methods. Our method is also advantageous over traditional methods in offering more informative, context-aware refusals, and achieves these benefits while only tuning less than 6% of the original parameters. SafeSwitch demonstrates large language models' capacity for self-awareness and reflection regarding safety, offering a promising approach to more nuanced and effective safety controls.

SafeSwitch: Steering Unsafe LLM Behavior via Internal Activation Signals

Hit identification is a central challenge in early drug discovery, traditionally requiring substantial experimental resources. Recent advances in artificial intelligence, particularly large language models (LLMs), have enabled virtual screening methods that reduce costs and improve efficiency. However, the growing complexity of these tools has limited their accessibility to wet-lab researchers. Multi-agent systems offer a promising solution by combining the interpretability of LLMs with the precision of specialized models and tools. In this work, we present MADD, a multi-agent system that builds and executes customized hit identification pipelines from natural language queries. MADD employs four coordinated agents to handle key subtasks in de novo compound generation and screening. We evaluate MADD across seven drug discovery cases and demonstrate its superior performance compared to existing LLM-based solutions. Using MADD, we pioneer application of AI-first drug design to five biological targets and release the identified hit molecules. Finally, we introduce a new benchmark of query-molecule pairs and docking scores for over three million compounds to contribute to the agentic future of drug design.

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LLM Jailbreak Detection for (Almost) Free!

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