Austria

Automatic fact verification systems increasingly rely on large language models (LLMs). We investigate how parametric knowledge biases in these models affect fact-checking outcomes of the HerO system (baseline for FEVER-25). We examine how the system is affected by: (1) potential bias in Llama 3.1&#39;s parametric knowledge and (2) intentionally injected bias. When prompted directly to perform fact-verification, Llama 3.1 labels nearly half the claims as &quot;Not Enough Evidence&quot;. Using only its parametric knowledge it is able to reach a verdict on the remaining half of the claims. In the second experiment, we prompt the model to generate supporting, refuting, or neutral fact-checking documents. These prompts significantly influence retrieval outcomes, with approximately 50% of retrieved evidence being unique to each perspective. Notably, the model sometimes refuses to generate supporting documents for claims it believes to be false, creating an inherent negative bias. Despite differences in retrieved evidence, final verdict predictions show stability across prompting strategies. The code is available at: \url{https://github.com/eibakke/FEVER-8-Shared-Task}

ACL 2025

(Fact) Check Your Bias

Automatic fact verification systems increasingly rely on large language models (LLMs). We investigate how parametric knowledge biases in these models affect fact-checking outcomes of the HerO system (baseline for FEVER-25). We examine how the system is affected by: (1) potential bias in Llama 3.1's parametric knowledge and (2) intentionally injected bias. When prompted directly to perform fact-verification, Llama 3.1 labels nearly half the claims as "Not Enough Evidence". Using only its parametric knowledge it is able to reach a verdict on the remaining half of the claims. In the second experiment, we prompt the model to generate supporting, refuting, or neutral fact-checking documents. These prompts significantly influence retrieval outcomes, with approximately 50% of retrieved evidence being unique to each perspective. Notably, the model sometimes refuses to generate supporting documents for claims it believes to be false, creating an inherent negative bias. Despite differences in retrieved evidence, final verdict predictions show stability across prompting strategies. The code is available at: \url{https://github.com/eibakke/FEVER-8-Shared-Task}

workshop paper

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

While Large Language Models (LLMs) with retrieval augmented generation (RAG) capabilities are increasingly used to verify information, their reliability for political fact-checking remains questionable. We present a comprehensive evaluation of eight state-of-the-art LLMs on their ability to fact-check political statements related to the 2024 U.S. presidential election. Using a dataset of 1,374 statements derived from 530 original claims fact-checked by major organizations in the run-up to the elections, we test both original and reformulated versions of statements. Our findings reveal that even the best-performing models achieve only modest accuracy (macro F1 score of 0.51), with RAG providing minimal improvements over models without search capabilities. Models particularly struggle with nuanced "misleading" statements and demonstrate poor robustness to reformulations. These results indicate that users relying on LLMs for political fact-checking are likely to receive inconsistent and sometimes incorrect assessments, even for statements that have been previously fact-checked by professional organizations and are readily available online.

RAG Is Not Enough: Evidence of Fact-Checking Limitations During the 2024 U.S. Presidential Elections

Automated fact-checking (AFC) of factual claims require efficiency and accuracy. Existing evaluation frameworks like Ev2R achieve strong semantic grounding but incur substantial computational cost, while simpler metrics based on overlap or one-to-one matching often misalign with human judgments. In this paper, we introduce SemQA, a lightweight and accurate evidence-scoring metric that combines transformer-based question scoring with bidirectional NLI entailment on answers. We evaluate SemQA by conducting human evaluations, analyzing correlations with existing metrics, and examining representative examples.

SemQA: Evaluating Evidence with Question Embeddings and Answer Entailment for Fact Verification

Given the limited computational and financial resources of news agencies, real-life usage of fact-checking systems requires fast response times. For this reason, our submission to the FEVER-8 claim verification shared task focuses on optimizing the efficiency of such pipelines built around subtasks such as evidence retrieval and veracity prediction. We propose the Semantic Filtering for Efficient Fact Checking (SFEFC) strategy, which is inspired by the FEVER-8 baseline and designed with the goal of reducing the number of LLM calls and other computationally expensive subroutines. Furthermore, we explore the reuse of cosine similarities initially calculated within a dense retrieval step to retrieve the top 10 most relevant evidence sentence sets. We use these sets for semantic filtering methods based on similarity scores and create filters for particularly hard classification labels "Not Enough Information" and "Conflicting Evidence/Cherrypicking" by identifying thresholds for potentially relevant information and the semantic variance within these sets. Compared to the parallelized FEVER-8 baseline, which takes 33.88 seconds on average to process a claim according to the FEVER-8 shared task leaderboard, our non-parallelized system remains competitive in regard to AVeriTeC retrieval scores while reducing the runtime to 7.01 seconds, achieving the fastest average runtime per claim.

Exploring Semantic Filtering Heuristics For Efficient Claim Verification

With the growing volume of misinformation online, automated fact-checking systems are becoming increasingly important. This paper presents SANCTUARY, an efficient pipeline for evidence-based verification of real-world claims. Our approach consists of three stages: Hypothetical Question & Passage Generation, a two-step Retrieval-Augmented Generation (RAG) hybrid evidence retrieval, and structured reasoning and prediction, which leverages two lightweight Large Language Models (LLMs). On the challenging AVeriTeC benchmark, our system achieves 25.27 points on the new AVeriTeC score (Ev2R recall), outperforming the previous state-of-the-art baseline by 5 absolute points (1.25× relative improvement). Sanctuary demonstrates that careful retrieval, reasoning strategies and well-integrated language models can substantially advance automated fact-checking performance.

SANCTUARY: An Efficient Evidence-based Automated Fact Checking System

In this paper, we present our fact-checking pipeline which has scored first in FEVER 8 shared task. Our fact-checking system is a simple two-step RAG pipeline based on our last year's submission. We show how the pipeline can be redeployed on-premise, achieving state-of-the-art fact-checking performance (in sense of Ev2R test-score), even under the constraint of a single Nvidia A10 GPU, 23GB of graphical memory and 60s running time per claim.

AIC CTU@FEVER 8: On-premise fact checking through long context RAG

With rapid advancements in large language models (LLMs) across artificial intelligence, machine learning, and data sci-ence, there is a growing need for evaluation frameworks that go beyond traditional performance metrics. Conventional methods focus mainly on accuracy and computational metrics, often neglecting user experience and community interaction—key elements in open-source environments. This paper intro-duces a multi-dimensional, user-centered evaluation frame-work, integrating metrics like User Engagement Index (UEI), Community Response Rate (CRR), and a Time Weight Factor (TWF) to assess LLMs' real-world impact. Additionally, we propose an adaptive weighting mechanism using Bayesian op-timization to dynamically adjust metric weights for more ac-curate model evaluation. Experimental results confirm that our framework effectively identifies models with strong user engagement and community support, offering a balanced, data-driven approach to open-source LLM evaluation. This frame-work serves as a valuable tool for developers and researchers in selecting and improving open-source models.

Multi-Dimensional Evaluation of Open-Source Language Models: Based on Machine Learning and Bayesian Optimization

Spatial representations are fundamental to human cognition, as understanding spatial relationships between objects is essential in daily life. Language serves as an indispensable tool for communicating spatial information, creating a close connection between spatial representations and spatial language. Large language models (LLMs), theoretically, possess spatial cognition due to their proficiency in natural language processing. This study examines the spatial representations of LLMs by employing traditional spatial tasks used in human experiments and comparing the models' performance to that of humans. The results indicate that LLMs resemble humans in selecting spatial prepositions to describe spatial relationships and exhibit a preference for vertically oriented spatial terms. However, the human tendency to better represent locations along specific axes is absent in the performance of LLMs. This finding suggests that, although spatial language is closely linked to spatial representations, the two are not entirely equivalent.

Spatial Representation of Large Language Models in 2D Scene

This paper presents a novel methodology for generating synthetic Preference Optimization (PO) datasets using multi-model workflows. We evaluate the effectiveness and potential of these workflows in automating and enhancing the dataset generation process. PO dataset generation requires two modules: (1) $\textit{response evaluation}$, and (2) $\textit{response generation}$. In the $\textit{response evaluation}$ module, the responses from Large Language Models (LLMs) are evaluated and ranked - a task typically carried out by human annotators that we automate using LLMs. We assess the response evaluation module in a 2 step process. In step 1, we assess LLMs as evaluators using three distinct prompting strategies. In step 2, we apply the winning prompting strategy to compare the performance of LLM-as-a-Judge, LLMs-as-a-Jury, and LLM Debate. Our evaluation shows that GPT-4o-as-a-Judge is more consistent across all datasets. For the $\textit{response generation}$ module, we use the identified LLM evaluator configuration and compare different configurations of the LLM Feedback Loop. We use the win rate to determine the best multi-model configuration for generation. Experimenting with various configurations, we find that the LLM Feedback Loop, with Llama as the generator and Gemma as the reviewer, achieves a notable 71.8\% and 73.8\% win rate over single-model Llama and Gemma, respectively. After identifying the best configurations for both modules, we generate our PO datasets using the above pipeline.

The Fellowship of the LLMs: Multi-Model Workflows for Synthetic Preference Optimization Dataset Generation

Free-text rationales justify model decisions in natural language and thus become likable and accessible among approaches to explanation across many tasks. However, their effectiveness can be hindered by misinterpretation and hallucination. As a perturbation test, we investigate how large language models (LLMs) perform rationale generation under the effects of readability level control, i.e., being prompted for an explanation targeting a specific expertise level, such as sixth grade or college. We find that explanations are adaptable to such instruction, though the observed distinction between readability levels does not fully match the defined complexity scores according to traditional readability metrics. Furthermore, the generated rationales tend to feature medium level complexity, which correlates with the measured quality using automatic metrics. Finally, our human annotators confirm a generally satisfactory impression on rationales at all readability levels, with high-school-level readability being most commonly perceived and favored.

Free-text Rationale Generation under Readability Level Control

A frequently observed problem with LLMs is their tendency to generate output that is nonsensical, illogical, or factually incorrect, often referred to broadly as “hallucination”. Building on the recently proposed HalluciGen task for hallucination detection and generation, we evaluate a suite of open-access LLMs on their ability to detect intrinsic hallucinations in two conditional generation tasks: translation and paraphrasing. We study how model performance varies across tasks and languages and we investigate the impact of model size, instruction-tuning, and prompt choice. We find that performance varies across models but is consistent across prompts. Finally, we find that NLI models perform comparably well, suggesting that LLM-based detectors are not the only viable option for this specific task.

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