United States

Long-form question answering (LFQA) demands nuanced evaluation of multi-sentence explanatory responses, yet existing metrics often fail to reflect human judgment. We present LFQA-HP-1M, a large-scale dataset comprising 1.3M human pairwise preference annotations for LFQA. We propose nine rubrics for answer quality evaluation, and show that simple linear models based on these features perform comparably to state-of-the-art LLM evaluators. We further examine transitivity consistency, positional bias, and verbosity biases in LLM evaluators and demonstrate their vulnerability to adversarial perturbations. Overall, this work provides one of the largest public LFQA preference datasets and a rubric-driven framework for transparent and reliable evaluation.

ACL 2026

LFQA-HP-1M: A Large-Scale Human Preference Dataset for Long-Form Question Answering

human preference modeling

long-form question answering (lfqa)

llm-as-a-judge

2021 Annual Conference of the North American Chapter of the Association for Computational Linguistics.

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NAACL 2021

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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.

We present NanoFlux, a novel adversarial framework for generating targeted training data to improve LLM reasoning, where adversarially-generated datasets of $\leq 200$ examples outperform conventional fine-tuning approaches. The framework employs a competitive dynamic between models alternating as Attacker and Defender, supervised by a tool-augmented Judge, synthesizing multi-step questions with explanatory annotations. Fine-tuning a 4B-parameter model on NanoFlux-generated data yields performance gains across diverse domains compared to full-benchmark fine-tuning: +5.9\% on mathematical reasoning, +3.6\% on scientific reasoning, and +16.6\% on medical reasoning, while reducing computational requirements by 3-14×. Ablation studies reveal a non-monotonic relationship between dataset characteristics and model performance, uncovering domain-specific optimal points for question complexity and reasoning quality. NanoFlux automates training data generation through embedding-based novelty filtering, tool-augmented evaluation, and multi-hop reasoning, pointing to the value of small, targeted training datasets.

NanoFlux: Adversarial Dual-LLM Evaluation and Distillation for Multi-Domain Reasoning

We provide a comprehensive review of the FRUIT (Faithfully Reflecting Updated Information in Text) task, which formalizes the challenge of accurately updating textual information with large language models (LLMs). Our work begins with an in-depth analysis of the FRUIT dataset, revealing key structural insights. We also investigate the unsupervised capabilities of LLMs—such as zero-shot learning, chain-of-thought reasoning, self-reflection, and evidence ordering. Experimental results demonstrate that unsupervised approaches perform competitively with supervised methods in faithful text updating. Qualitative analysis shows that updates utilizing table-structured evidence outperform those based on unstructured text. We also discuss important limitations, including the need for new datasets and the risks of information leakage in this domain. These findings have significant implications for applications requiring precise document updates, such as software engineering, technical documentation, and legal document maintenance.

Evaluating the Reliability of LLMs in Faithfully Updating Text: An Empirical Study

Contextual text classification with BERT typically relies on the [CLS] token representation for downstream prediction. While effective under standard conditions, [CLS]-based pooling is brittle under adversarial perturbation, as its single-vector representation is indiscriminately influenced by injected adversarial tokens. We propose Per-Dimension Top-K Average Pooling, a pooling strategy that, for each hidden dimension, selectively aggregates only the top-K token activations rather than the full sequence — effectively controlling which tokens contribute to the final representation. This token-level selectivity acts as a natural filter against adversarial injection: tokens that do not rank among the top-K for a given dimension are suppressed from aggregation. We evaluate our approach against CLS, Global Average Pooling (GAP), Global Max Pooling (GMP), and Hybrid variants across three text classification domains: spam detection (Enron and LingSpam), automated essay scoring (ASAP), and hate speech classification. On the Enron spam dataset under adversarial attack, our best Hybrid (K=3) variant reduces the Attack Success Rate from 70.65\% to 37.07\% while maintaining clean accuracy above 99\%, compared to CLS which degrades to 63.64\% adversarial accuracy. Representation-level analyses further corroborate these findings: Top-K pooling variants exhibit substantially lower cosine similarity shift under attack, and adversarially injected tokens enter the top-K selection in far fewer dimensions compared to CLS. These results suggest that per-dimension token selectivity offers a principled and lightweight mechanism for adversarial robustness in BERT-based classifiers without any modification to the underlying model architecture.

Not All Tokens Are Equal: Per-Dimension Top-K Pooling for Adversarially Robust BERT Classification

Agentic systems for business process automation often require compliance with policies governing conditional updates to the system state. Evaluation of policy adherence in LLM-based agentic workflows is typically performed by comparing the final system state against a predefined ground truth. While this approach detects explicit policy violations, it may overlook a more subtle class of issues in which agents bypass required policy checks, yet reach a correct outcome due to favorable circumstances. We refer to such cases as \textit{near-misses} or \textit{latent failures}. In this work, we introduce a novel metric for detecting latent policy failures in agent conversations traces. Building on the ToolGuard framework, which converts natural-language policies into executable guard code, our method analyzes agent trajectories to determine whether agent's tool-calling decisions where sufficiently informed. We evaluate our approach on the $\tau^2$-verified Airlines benchmark across several contemporary open and proprietary LLMs acting as agents. Our results show that latent failures occur in 8--17\% of trajectories involving mutating tool calls, even when the final outcome matches the expected ground-truth state. These findings reveal a blind spot in current evaluation methodologies and highlight the need for metrics that assess not only final outcomes but also the decision process leading to them.

Near-Miss: Latent Policy Failure Detection in Agentic Workflows

Curriculum learning trains models by progressively introducing examples from easy to difficult. While effective, two key challenges remain: how to define example difficulty and how to schedule training data appropriately. We present PUDF, a framework that addresses both challenges using Item Response Theory (IRT). First, IRT-AC estimates global, model-independent difficulty parameters for training examples by fitting an IRT model to response patterns from an artificial crowd of diverse LLMs. Second, DDS-MAE estimates model ability on the same IRT scale during each training epoch and selects training data accordingly. Experiments with Llama 3.1-8B and Qwen 2.5-7B across GLUE, AG News, MedQA, and GSM8K show that PUDF consistently improves accuracy and reduces training time by up to 70%, outperforming state-of-the-art curriculum learning methods.

A Psychology-based Unified Dynamic Framework for Curriculum Learning

How should we evaluate generation systems that combine autoregressive (AR) and diffusion decoding? We study this question through *Speculative Refinement* (SpecRef), a training-free hybrid method that warm-starts a masked diffusion language model from an AR draft using entropy-guided selective masking. Evaluating SpecRef across six benchmarks (HumanEval, MBPP, GSM8K, BBH, ARC-Challenge, HellaSwag) with three distinct evaluation protocols (execution-based pass@1, exact-match, log-likelihood scoring), we surface several findings relevant beyond our specific system: (1) code benchmarks conflate structural discovery} with logical correctness: providing a syntactic scaffold lifts accuracy from near zero to over 20\% without changing the model, indicating that much of the baseline failure is structural; (2) a *refinement tension* phenomenon where multi-stage correction degrades already-correct tokens, exposing benchmark saturation ceilings invisible to single-model evaluation; (3) log-likelihood and generative evaluation produce different model rankings for the same model pair, suggesting they measure different capabilities; (4) standard Python post-processing silently breaks code evaluation for non-AR generators. These observations apply to any multi-stage or non-autoregressive generation pipeline and point toward more diagnostic evaluation practices.

Speculative Refinement: A Hybrid Autoregressive Diffusion Decoding Strategy and Its Behavior Across Benchmarks

With the growing need for evaluating Large Language Models (LLMs) and their applications to speech, challenges persist in summarizing and evaluating conversations that lack a clear end goal. We introduce SAUCE -- a reference-free, fact-based evaluation pipeline for cross-lingual conversational speech summarization. It measures the accuracy and the fact coverage of a summary through the entailment between conversation and text. We compare SAUCE against several popular summarization metrics and demonstrate the effectiveness of capturing information loss due to transcription and translation error and identifying broken summaries. Crucially, unlike black-box LLM evaluators or dense embedding metrics, SAUCE is inherently explainable: it maps summary scores to discrete, verifiable facts, allowing users to pinpoint exact hallucinations or omissions. We illustrate how this interpretability helps developers systematically profile LLM behaviors and gives end-users an actionable tool to verify summary accuracy in noisy, real-world conditions. Preliminary investigations show SAUCE strongly align with human judgment.

SAFE: Summary Analysis via Fact Entailment for Cross-Lingual Conversational Speech Summarization

Evaluating automatic speech recognition (ASR) quality in production is a fundamentally challenging problem, owing to the volume and variability of real-time user interactions, thus making traditional methods impractical, and ground-truth annotations are typically unavailable at scale. We propose a large-scale evaluation pipeline that enables ASR quality evaluation via weakly supervised estimations derived from multiple independent ASR engines. The proxy estimations’ outputs are used to compute consensus-driven metrics such as word error rate (WER), character error rate (CER), and semantic divergence – to estimate transcription quality across varied query categories. These signals form the basis for a large language model (LLM)-driven insight agent, and custom tools to detect failure patterns, extract usage trends and behaviors, and provide actionable insights. This framework serves as a final layer of evaluation, which acts as an independent module compatible with any ASR system, regardless of its underlying architecture. By processing millions of queries periodically without manual intervention, this solution provides actionable insights that support the research and product team with valuable feedback for continuous improvement.

Evaluating ASR Quality at Scale on TV Entertainment Platforms

Multi-hop question answering is widely used to evaluate the reasoning capabilities of large language models (LLMs), as it requires integrating multiple pieces of supporting knowledge to arrive at a correct answer. While prior work has compared fine-tuning and retrieval-augmented generation (RAG) for factual recall and single-hop question answering, it remains unclear how these approaches perform in multi-hop settings that require compositional reasoning over temporally novel knowledge. In particular, prior comparisons often do not control for model scale, evaluation format, or knowledge freshness, making it difficult to isolate the effect of knowledge injection mechanisms. In this paper, we systematically compare parametric and non-parametric knowledge injection methods for open-domain multi-hop question answering. We evaluate unsupervised fine-tuning (continual pretraining), supervised fine-tuning, and retrieval-augmented generation across three 7B-parameter open-source LLMs. Experiments are conducted on two benchmarks: Question Answering Science Challenge (QASC), a standard multi-hop science question answering dataset, and a newly constructed dataset of over 10,000 multi-hop questions derived from Wikipedia events in 2024, which is designed to test knowledge beyond the models’ pretraining cutoff. Our results show that unsupervised fine-tuning provides only limited gains over base models, suggesting that continual pretraining alone is insufficient for improving multi-hop reasoning accuracy. In contrast, RAG yields substantial and consistent improvements, particularly when answering questions that rely on temporally novel information. Supervised fine-tuning achieves the highest overall accuracy across models and datasets. These findings highlight fundamental differences in how knowledge injection mechanisms support multi-hop question answering and underscore the importance of retrieval-based methods when external or compositional knowledge is required.

Fine-Tuning vs. RAG for Multi-Hop Question Answering with Novel Knowledge

Large language models (LLMs) are increasingly used in the mental health domain, yet it remains unclear how well they capture related biomedical knowledge and how reliably they apply it to clinically salient structured judgments. Here, we present a knowledge-graph (KG)-grounded benchmark for assessing LLMs on mental-health entity recognition, relation judgment, and two-hop reasoning. The benchmark is derived from PrimeKG and comprises nine task families with KG-supported answers and controlled negative options. Experiments across 15 closed- and open-source LLMs reveal a persistent recognition-to-judgment gap: leading models achieve near-ceiling performance on entity typing and on the small relation-typing subset, yet they still struggle with relation prediction and two-hop reasoning. Additionally, short KG-derived snippets benefit some models but degrade performance for others. Moreover, output-format reliability can substantially influence measured performance under constrained multiple-choice settings, highlighting the critical role of response validity in benchmark-based evaluation. MHGraphBench should therefore be interpreted as evaluating agreement with a curated mental-health slice of PrimeKG under a constrained multiple-choice interface, rather than as a direct assessment of real-world clinical safety.

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