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LLM-based agents can complete tasks correctly yet still frustrate users through poor interaction patterns, such as excessive confirmations, opaque reasoning, or misaligned pacing. Current benchmarks evaluate task accuracy but overlook how agents interact: whether they infer preferences from implicit cues, adapt dynamically, or maintain fine-grained interaction quality. We introduce \prefix, a configurable environment that evaluates both what agents accomplish and how they interact. Central to \prefix~is the Interaction-as-a-Tool (IaaT) paradigm, which treats interaction behaviors as structured tool calls, unifying them with existing evaluation frameworks. We define 31 preference settings across 14 attributes and formalize user experience (UX) as a core metric alongside task accuracy. A composite LLM-as-a-Judge mechanism across seven UX dimensions achieves strong aggregate reliability (ICC $&gt;$ 0.79), high internal consistency ($\alpha$ = 0.943), and human correlation ($\rho$ = 0.52-0.78). Preference-aware agents show 7.6\% average UX improvement and 18.5\% gain in preference alignment.

ACL 2026

PrefIx: Understand and Adapt to User Preference in Human-Agent Interaction

The UKSG Annual Conference and Exhibition 2021 will be held online for the first time. The event is a major event in the scholarly communications calendar which attracts a large number of delegates each year from around the world - librarians, publishers, content providers, consultants and intermediaries. The conference combines high-quality plenary presentations, lightning talks and breakout sessions with virtual social events and a major online trade exhibition.



UKSG Annual Conference 2021

 UKSG Annual Conference is a major event in the scholarly communications calendar which attracts a large number of delegates each year from around the world - librarians, publishers, content providers, consultants and intermediaries. 

LLM-based agents can complete tasks correctly yet still frustrate users through poor interaction patterns, such as excessive confirmations, opaque reasoning, or misaligned pacing. Current benchmarks evaluate task accuracy but overlook how agents interact: whether they infer preferences from implicit cues, adapt dynamically, or maintain fine-grained interaction quality. We introduce \prefix, a configurable environment that evaluates both what agents accomplish and how they interact. Central to \prefix~is the Interaction-as-a-Tool (IaaT) paradigm, which treats interaction behaviors as structured tool calls, unifying them with existing evaluation frameworks. We define 31 preference settings across 14 attributes and formalize user experience (UX) as a core metric alongside task accuracy. A composite LLM-as-a-Judge mechanism across seven UX dimensions achieves strong aggregate reliability (ICC $>$ 0.79), high internal consistency ($\alpha$ = 0.943), and human correlation ($\rho$ = 0.52-0.78). Preference-aware agents show 7.6\% average UX improvement and 18.5\% gain in preference alignment.

poster

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

While Large Language Models (LLMs) have emerged as powerful foundational models to solve a variety of tasks, they have also been shown to be prone to hallucinations, i.e., generating responses that sound confident but are actually incorrect or even nonsensical. Existing hallucination detectors propose a wide range of empirical scoring rules, but their performance varies across models and datasets, and it is hard to determine which ones to rely on in practice or to treat as a reliable detector. In this work, we formulate the problem of detecting hallucinations as a hypothesis testing problem and draw parallels with the problem of out-of-distribution detection in machine learning models. We then propose a multiple-testing-inspired method that systematically aggregates multiple evaluation scores via conformal p-values, enabling calibrated detection with controlled false alarm rate. Extensive experiments across diverse models and datasets validate the robustness of our approach against state-of-the-art methods.

 Principled Detection of Hallucinations in Large Language Models via Multiple Testing

Large language models (LLMs) are increasingly deployed in monetization-driven systems such as search engines, advertising platforms, and e-commerce services, where decision making is shaped by complex interactions among user intent, advertiser objectives, and platform constraints. Despite rapid progress, existing benchmarks primarily focus on shopping-centric scenarios and user-facing data, capturing only a limited subset of real-world monetization pipelines and overlooking intermediate decision stages and robustness considerations. In this work, we introduce MonBench, a high-quality multi-task benchmark designed to evaluate LLMs in realistic monetization contexts. The benchmark is constructed from large-scale production data collected from multiple search engines, including both intermediate candidate pools and user-visible outcomes, better reflecting the distributional characteristics of real monetization systems. MonBench covers key capability dimensions such as intent understanding, commercial matching, and user behavior modeling, and adopts a unified multiple-choice formulation to enable systematic comparison across models. We further propose a comprehensive evaluation protocol that measures both performance and robustness. We evaluate a diverse set of state-of-the-art LLMs and conduct detailed task-level analyses. Our results reveal monetization-specific behaviors, including gaps between relevance optimization and broader decision-making capabilities, as well as differences in robustness across model families. These findings provide new insights into the strengths and limitations of current LLMs and highlight the need for richer domain-specific supervision in monetization-oriented applications.

Is Your Language Model Ready for Monetization Decisions?

Retrieval-Augmented Generation (RAG) provides external knowledge support for large language models (LLMs) in medical applications, but retrieved contexts often contain noisy or conflicting evidence that can degrade reasoning. We observe that when internal and external knowledge disagree, models systematically prefer external citations, inadvertently injecting retrieval noise. Our analyses further show that only a subset of retrieved citations consistently improves outcomes; these effective citations exhibit markedly lower token-level entropy, linking citation entropy to model accuracy. Building on these findings, we propose a complete pipeline consisting of a training-free multi-turn reasoning framework and a post-training methodology. The training-free framework elicits internal thought, external thought, and fusion thought, and applies conflict detection and explicit denoising for complex queries. For post-training, we distill structured supervised fine-tuning (SFT) data and apply GRPO with an entropy-based citation reward that encourages selective citation of beneficial external knowledge while penalizing noisy citations. Experiments across diverse benchmarks demonstrate consistent gains in noise-resistant medical reasoning, with larger improvements on harder cases.

Not All Citations Are Equal:Entropy-Guided Citation Selection for Noise-Resistant Medical LLM

Recent advances in summary evaluation are based on model-based metrics to assess quality dimensions, such as completeness, conciseness, and faithfulness. However, these methods often require large language models, and predicted scores are frequently miscalibrated, limiting their reliability. Moreover, evaluating the average quality across different summaries for a single document typically requires access to multiple reference summaries. Here, we propose a general framework that generates individual and average proxy scores without relying on reference summaries, human annotations, or expensive model-based metrics. We also propose group isotonic regression binning (GIRB), a calibration method that adjusts the raw predictions to better align with ground-truth evaluation metrics. While we focus on continuous-value scenarios, such as summarization, the method is applicable to discrete-value tasks, such as question answering. Experiments on seven datasets demonstrate that our approach consistently outperforms existing baselines.

Calibrating Model-Based Evaluation Metrics for Summarization

Caregivers seeking AI-mediated support express complex needs---information-seeking, emotional validation, and distress cues---that warrant careful evaluation of response safety and appropriateness. Existing AI evaluation frameworks, primarily focused on general risks (toxicity, hallucinations, policy violations, etc) may not adequately capture the nuanced risks of LLM-responses in caregiving-contexts. We introduce RubRIX (Rubric-based Risk Index), a theory-driven, clinician-validated framework for evaluating risks in LLM caregiving responses. Grounded in the Elements of an Ethic of Care, RubRIX operationalizes five empirically-derived risk dimensions: Inattention, Bias & Stigma, Information Inaccuracy, Uncritical Affirmation, and Epistemic Arrogance. We evaluate six state-of-the-art LLMs on over 20,000 caregiver queries from Reddit and ALZConnected. Rubric-guided refinement consistently reduced risk-components by 45-98% after one iteration across models. This work contributes a methodological approach for developing domain-sensitive, user-centered evaluation frameworks for high-burden contexts. Our findings highlight the importance of domain-sensitive, interactional risk evaluation for the responsible deployment of LLMs in caregiving support contexts. We release benchmark datasets to enable future research on contextual risk evaluation in AI-mediated support.

 RubRIX: Rubric-Driven Risk Mitigation in Caregiver-AI Interactions

Retrieval-Augmented Generation (RAG) enhances Large Language Models (LLMs) by incorporating external knowledge, effectively mitigating their inherent knowledge limitations. However, RAG remains vulnerable to poisoning attacks that manipulate retrieved texts to mislead model outputs. Existing defense mechanisms often lack theoretical robustness guarantees and perform unreliably when the LLM has limited knowledge of the retrieved content. In this work, we propose PRA-RAG, a provably robust retrieval aggregation algorithm designed to defend against poisoning attacks on retrieved texts. PRA-RAG samples multiple combinations of retrieved texts and utilizes geometric structures in the embedding space to identify a robust subset, from which a stable aggregated representation is derived. We provide theoretical bounds on the maximum impact of poisoned retrieved content and establish a quantitative measure of RAG’s robustness. Experiments across multiple benchmarks and RAG architectures demonstrate that PRA-RAG reduces the attack success rate to as low as 1% while maintaining an accuracy of 71%, significantly outperforming representative state-of-the-art (SOTA) methods.

PRA-RAG: Provably Robust Aggregation in Retrieval-Augmented Generation against Retrieval Corruption

Writing a literature review requires a deep understanding of the relationships among cited papers: how they build on, challenge, or offer alternative perspectives to one another. We present Graph-Reasoning Aided Survey Planning (GRASP), a framework combining LLM planning for related work generation with graph algorithms to extract key relationships among cited papers. Our two-layer graph structure consists of a Graph of Thoughts and an Argument-Counteragument Planning Network, representing the cited papers at different levels of granularity, and we apply topology-aware pruning via a Steiner tree to identify the core inter-paper relationships captured in our graph. Our citation analysis-based evaluation shows that GRASP generates RWS that closely match human-written targets in terms of the discourse roles, intents, and grouping of citations.

GRASP: Graph-Reasoning Aided Survey Planning for High-Fidelity Related Work Generation

Toxic language includes content that is offensive, abusive, or that promotes harm. Progress in preventing toxic output from large language models (LLMs) is hampered by inconsistent definitions of toxicity. We introduce TRuST, a large-scale dataset that unifies and expands prior resources through a carefully synthesized definition of toxicity, and corresponding annotation scheme. It consists of ∼300k annotations, with high-quality human annotation on ∼11k. To ensure high-quality, we designed a rigorous, multi-stage human annotation process, and evaluated the diversity of the annotators. Then we benchmarked state-of-the-art LLMs and pre-trained models on three tasks: toxicity detection, identification of the target group, and of toxic words. Our results indicate that fine-tuned PLMs outperform LLMs on the three tasks, and that current reasoning models do not reliably improve performance. TRuST constitutes one of the most comprehensive resources for evaluating and mitigating LLM toxicity, and other research in socially-aware and safer language technologies.

Something Just Like TRuST ♪ *: Toxicity Recognition of Span and Target

Metaphors are powerful framing devices, yet their source domains alone do not fully explain the specific associations they evoke. We argue that the interplay between source domains and semantic frames determines how metaphors shape understanding of complex issues, and present a computational framework that allows to derive salient discourse metaphors through their source domains and semantic frames. Applying this framework to climate change news, we uncover not only well-known source domains but also reveal nuanced frame-level associations that distinguish how the issue is portrayed. In analyzing immigration discourse across political ideologies, we demonstrate that liberals and conservatives systematically employ different semantic frames within the same source domains, with conservatives favoring frames emphasizing uncontrollability and liberals choosing neutral or more ``victimizing'' semantic frames. Our work bridges conceptual metaphor theory and linguistics, providing the first NLP approach for discovery of discourse metaphors and fine-grained analysis of differences in metaphorical framing.

Not all ANIMALs are equal: metaphorical framing through source domains and semantic frames

Small language models (SLMs), such as BART, can achieve summarization performance comparable to large language models (LLMs) via distillation. However, existing LLM-based ranking strategies for summary candidates suffer from instability, while classical metrics (e.g., ROUGE) are insufficient to rank high-quality summaries. To address these issues, we introduce SCURank, a framework that enhances summarization by leveraging Summary Content Units (SCUs). Instead of relying on unstable comparisons or surface-level overlap, SCURank evaluates summaries based on the richness and semantic importance of information content. We investigate the effectiveness of SCURank in distilling summaries from multiple diverse LLMs. Experimental results demonstrate that SCURank outperforms traditional metrics and LLM-based ranking methods across evaluation measures and datasets. Furthermore, our findings show that incorporating diverse LLM summaries enhances model abstractiveness and overall distilled model performance, validating the benefits of information-centric ranking in multi-LLM distillation.

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