Austria

We introduce the concept of context-driven over-refusal, an abstention arising when model&#39;s safety guardrails are triggered by the grounding knowledge provided alongside the user&#39;s request. Distinct from question-driven over-refusal, this occurs in both retrieval-augmented generation (RAG) and natural language processing (NLP) task completion (e.g. summarization, translation) where external content can unexpectedly trigger refusals. In this work, we present a novel two-stage evaluation framework named COVER, designed to quantify and analyze this behavior. Through a comprehensive empirical study on two public corpora, we show that over-refusal rates strongly depend on the task, system prompts, model family, and the number of retrieved documents. We observe that tasks such as translation and summarization yield disproportionately high over-refusal rates, while question-answering remains relatively robust, especially in newer models. Moreover, increasing the number of contextual documents tends to reduce refusals, yet broadens the pool of prompts at risk of encountering at least one &quot;unsafe&quot; text. Interestingly, strict system prompts do not necessarily lead to higher over-refusal rates, suggesting that in the absence of explicit directives, some models may default to a more cautious behavior. These findings highlight the need for fine-grained alignment and benchmarking strategies sensitive to both user intent and contextual nuances, offering a roadmap for future research in model training and evaluation.

ACL 2025

COVER: Context-Driven Over-Refusal Verification in LLMs

over-refusal

ai safety

It is my great pleasure and honor to welcome you to the 64th Annual Meeting of the Association for Computational Linguistics (ACL 2026), held in San Diego, California, USA, July 2–7, 2026. ACL 2026 continues our fields tradition of excellence in scholarship, innovation, and inclusivity, and I am deeply grateful to the many volunteers who have worked tirelessly to bring this event to life.

It is exciting to see the many developments in the field reflected at our conference, such as the advancement of large language models (born out of our community) into many application directions. This is not without challenges, partly due to unsolved problems, and partly due to misuse of the technology. All this is reflected well at ACL 2026. The conference also reflects that the field is not only about advancing technology, but also the science of fundamentally understanding language and how it is use by many different speaker communities. 
[Full Message from General Chair Philipp Koehn](https://drive.google.com/file/d/1QiJFOmMjvDgsDo3i1XzlQnImxe3RU_Cy/view?usp=sharing) 
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ACL 2026

The 64th Annual Meeting of the Association for Computational Linguistics (ACL 2026) will take place in San Diego, California, from July 2 - 7, 2026.

We introduce the concept of context-driven over-refusal, an abstention arising when model's safety guardrails are triggered by the grounding knowledge provided alongside the user's request. Distinct from question-driven over-refusal, this occurs in both retrieval-augmented generation (RAG) and natural language processing (NLP) task completion (e.g. summarization, translation) where external content can unexpectedly trigger refusals. In this work, we present a novel two-stage evaluation framework named COVER, designed to quantify and analyze this behavior. Through a comprehensive empirical study on two public corpora, we show that over-refusal rates strongly depend on the task, system prompts, model family, and the number of retrieved documents. We observe that tasks such as translation and summarization yield disproportionately high over-refusal rates, while question-answering remains relatively robust, especially in newer models. Moreover, increasing the number of contextual documents tends to reduce refusals, yet broadens the pool of prompts at risk of encountering at least one "unsafe" text. Interestingly, strict system prompts do not necessarily lead to higher over-refusal rates, suggesting that in the absence of explicit directives, some models may default to a more cautious behavior. These findings highlight the need for fine-grained alignment and benchmarking strategies sensitive to both user intent and contextual nuances, offering a roadmap for future research in model training and evaluation.

poster

### Welcome to The 63rd Annual Meeting of the Association for Computational Linguistics (ACL 2025)

Message from the General Chair: 
*It is my great pleasure and honor to welcome you to the 63rd Annual Meeting of the Association for Computational Linguistics (ACL 2025), held in beautiful Vienna, Austria, from July 27 to August 1, 2025. ACL2025continues our field’s tradition of excellence in scholarship, innovation, and inclusivity, and I am deeply grateful to the many volunteers who have worked tirelessly to bring this event to life.* 
[Read more](https://drive.google.com/file/d/1GI_hvOpjswAuYdUTromfeDiPpCcqidwg/view?usp=sharing)

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Welcome to The 63rd Annual Meeting of the Association for Computational Linguistics (ACL 2025)

The dissemination of Large Language Models (LLMs), trained at scale, and endowed with powerful text-generating abilities, has made it easier for all to produce harmful, toxic, faked or forged content. In response, various proposals have been made to automatically discriminate artificially generated from human-written texts, typically framing the problem as a binary classification problem. Early approaches evaluate an input document with a well-chosen detector LLM, assuming that low-perplexity scores reliably signal machine-made content. More recent systems instead consider two LLMs and compare their probability distributions over the document to further discriminate when perplexity alone cannot. However, using a fixed pair of models can induce brittleness in performance. We extend these approaches to the ensembling of several LLMs and derive a new, theoretically grounded approach to combine their respective strengths. Our experiments, using a variety of generator LLMs, suggest that this approach effectively harnesses each model’s capabilities, leading to strong detection performance on a variety of domains.

MOSAIC: Multiple Observers Spotting AI Content

Despite the widespread use of English as a Second or Foreign Language (ESFL), developing syntactico-semantic representations for it is limited --- the irregularities in ESFL complicate systematic composition and subsequently the derivation of its semantics. This paper draws on constructivism and proposes a novel Synchronous Hyperedge Replacement Grammar (SHRG)-based constructivist approach to address the challenges. By using constructions as fundamental units, this approach not only accommodates both the idiosyncrasies and the compositional nature of ESFL, but also bridges the gap between literal cues and intended meaning. The feasibility of this constructivist approach is demonstrated using real ESFL data, resulting in a gold-standard, medium-sized syntactico-semantic bank that covers a wide range of ESFL phenomena. Experimental results further indicate that this newly developed resource significantly enhances syntactic parsing for ESFL, achieving an F_1 score improvement of over 20%.

Compositional Syntactico-SemBanking for English as a Second or Foreign Language

Tool learning aims to augment large language models (LLMs) with diverse tools, enabling them to act as agents for solving practical tasks. Due to the limited context length of tool-using LLMs, adopting information retrieval (IR) models to select useful tools from large toolsets is a critical initial step. However, the performance of IR models in tool retrieval tasks remains underexplored and unclear. Most tool-use benchmarks simplify this step by manually pre-annotating a small set of relevant tools for each task, which is far from the real-world scenarios. In this paper, we propose ToolRet, a heterogeneous tool retrieval benchmark comprising 7.6k diverse retrieval tasks, and a corpus of 43k tools, collected from existing datasets. We benchmark six types of models on ToolRet. Surprisingly, even the models with strong performance in conventional IR benchmarks, exhibit poor performance on ToolRet. This low retrieval quality degrades the task pass rate of tool-use LLMs. As a further step, we contribute a large-scale training dataset with over 200k instances, which substantially optimizes the tool retrieval ability of IR models.

Retrieval Models Aren’t Tool-Savvy: Benchmarking Tool Retrieval for Large Language Models

The rapid growth of social media platforms has raised significant concerns regarding online content toxicity. When Large Language Models (LLMs) are used for toxicity detection, two key challenges emerge: 1) the absence of domain-specific toxicity knowledge leads to false negatives; 2) the excessive sensitivity of LLMs to toxic speech results in false positives, limiting freedom of speech. To address these issues, we propose a novel method called *MetaTox*, leveraging graph search on a meta-toxic knowledge graph to enhance hatred and toxicity detection. First, we construct a comprehensive meta-toxic knowledge graph by utilizing LLMs to extract toxic information through a three step pipeline. Second, we query the graph via retrieval and ranking processes to supplement accurate, relevant toxicity knowledge. Extensive experiments and case studies across multiple datasets demonstrate that our MetaTox boosts overall toxicity detection performance, particularly in out-of-domain settings. In addition, under in-domain scenarios, we surprisingly find that small language models are more competent. Our code is available at https://github.com/YiboZhao624/MetaTox.

Enhancing LLM-based Hatred and Toxicity Detection with Meta-Toxic Knowledge Graph

As large language models (LLMs) are applied across diverse domains, the ability to selectively unlearn specific information has become increasingly essential. For instance, LLMs are expected to provide certain confidential information to authorized internal users, such as employees or trusted partners, while withholding it from external users, including the general public and unauthorized entities. In response to this challenge, we propose a novel method termed ''in-context knowledge unlearning'', which enables the model to selectively forget information in test-time based on the query context. Our method fine-tunes pre-trained LLMs to enable prompt unlearning of target knowledge within the context, while preserving other knowledge. Experiments on TOFU, AGE and RWKU datasets using Llama2-7B/13B and Mistral-7B models show that our method achieves up to 95% forget accuracy while retaining 80% of unrelated knowledge, significantly outperforming baselines in both in-domain and out-of-domain scenarios. Further investigation of the model's internal behavior revealed that while fine-tuned LLMs generate correct predictions in the middle layers and maintain them up to the final layer, they make the decision to forget at the last layer, i.e. ''LLMs pretend to forget''. Our findings offer valuable insight into the improvement of the robustness of the unlearning mechanisms in LLM, setting a foundation for future research in the field.

Answer When Needed, Forget When Not: Language Models Pretend to Forget via In-Context Knowledge Unlearning

In this paper, we present TituLLMs, the first large pretrained Bangla LLMs, available in 1b and 3b parameter sizes. Due to computational constraints during both training and inference, we focused on smaller models. To train TituLLMs, we collected a pretraining dataset of approximately ∼ 37 billion tokens. We extended the Llama-3.2 tokenizer to incorporate language- and culture-specific knowledge, which also enables faster training and inference. There was a lack of benchmarking datasets to benchmark LLMs for Bangla. To address this gap, we developed five benchmarking datasets. We benchmarked various LLMs, including TituLLMs, and demonstrated that TituLLMs outperforms its initial multilingual versions. However, this is not always the case, highlighting the complexities of language adaptation. Our work lays the groundwork for adapting existing multilingual open models to other low-resource languages. To facilitate broader adoption and further research, we have made the TituLLMs models and benchmarking datasets publicly available.

TituLLMs: A Family of Bangla LLMs with Comprehensive Benchmarking

Documents are fundamental to preserving and disseminating information, often incorporating complex layouts, tables, and charts that pose significant challenges for automatic document understanding (DU). While vision-language large models (VLLMs) have demonstrated improvements across various tasks, their effectiveness in processing long-context vision inputs remains unclear. This paper introduces WikiMixQA, a benchmark comprising 1,000 multiple-choice questions (MCQs) designed to evaluate cross-modal reasoning over tables and charts extracted from 4,000 Wikipedia pages spanning seven distinct topics. Unlike existing benchmarks, WikiMixQA emphasizes complex reasoning by requiring models to synthesize information from multiple modalities. We evaluate 12 state-of-the-art vision-language models, revealing that while proprietary models achieve ~70% accuracy when provided with direct context, their performance deteriorates significantly when retrieval from long documents is required. Among these, GPT-4-o is the only model exceeding 50% accuracy in this setting, whereas open-source models perform considerably worse, with a maximum accuracy of 27%. These findings underscore the challenges of long-context, multi-modal reasoning and establish WikiMixQA as a crucial benchmark for advancing document understanding research.

WikiMixQA: A Multimodal Benchmark for Question Answering over Tables and Charts

Large Language Models (LLMs) excel in various natural language tasks but often struggle with long-horizon planning problems requiring structured reasoning. This limitation has drawn interest in integrating neuro-symbolic approaches within the Automated Planning (AP) and Natural Language Processing (NLP) communities. However, identifying optimal AP deployment frameworks can be daunting. This paper aims to provide a timely survey of the current research with an in-depth analysis, positioning LLMs as tools for extracting and refining planning models to support reliable AP planners. By systematically reviewing the current state of research, we highlight methodologies, and identify critical challenges and future directions, hoping to contribute to the joint research on NLP and Automated Planning.

LLMs as Planning Modelers: A Survey for Leveraging Large Language Models to Construct Automated Planning Models

Ensuring the safety alignment of Large Language Models (LLMs) is critical for generating responses consistent with human values. However, LLMs remain vulnerable to jailbreaking attacks, where carefully crafted prompts manipulate them into producing toxic content. One category of such attacks reformulates the task as an optimization problem, aiming to elicit affirmative responses from the LLM. However, these methods heavily rely on predefined objectionable behaviors, limiting their effectiveness and adaptability to diverse harmful queries. In this study, we first identify why the vanilla target loss is suboptimal and then propose enhancements to the loss objective. We introduce DSN (Don’t Say No) attack, which combines a cosine decay schedule method with refusal suppression to achieve higher success rates. Extensive experiments demonstrate that DSN outperforms baseline attacks and achieves state-of-the-art attack success rates (ASR). DSN also shows strong universality and transferability to unseen datasets and black-box models.

Don't Say No: Jailbreaking LLM by Suppressing Refusal

As Large Language Models (LLMs) increasingly produce human-quality text, understanding how readers perceive and evaluate AI-generated literature becomes critical. This paper investigates the interplay between measurable textual features and reader preferences in the context of short stories. We analyze multiple datasets where readers (ranging from literary experts to lay audiences) evaluated both human-authored and LLM-generated texts. We propose to model reader's preferences as weighted combinations of intrinsic textual features such as coherence, sentiment volatility, thematic entropy, etc. Results show that (1) when LLM-generated text closely approximates the feature distributions of human text, readers struggle to distinguish them; (2) expert and non-expert readers prioritize distinctly different textual features, revealing systematic variations in literary judgment; and (3) these preference patterns are remarkably stable across diverse datasets. Our framework provides a step towards understanding and potentially tailoring AI-generated literature to meet the expectations of specific audiences.

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MOSAIC: Multiple Observers Spotting AI Content

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Please refuse to answer me! Mitigating Over-Refusal in Large Language Models via Adaptive Contrastive Decoding