When Models Lie, We Learn: Multilingual Span-Level Hallucination
  Detection with PsiloQA
Authors: name: Elisei Rykov, name: Kseniia Petrushina, name: Maksim Savkin, name: Valerii Olisov, name: Artem Vazhentsev, name: Kseniia Titova, name: Alexander Panchenko, name: Vasily Konovalov, name: Julia Belikova

Hallucination detection remains a fundamental challenge for the safe and
reliable deployment of large language models (LLMs), especially in applications
requiring factual accuracy. Existing hallucination benchmarks often operate at
the sequence level and are limited to English, lacking the fine-grained,
multilingual supervision needed for a comprehensive evaluation. In this work,
we introduce PsiloQA, a large-scale, multilingual dataset annotated with
span-level hallucinations across 14 languages. PsiloQA is constructed through
an automated three-stage pipeline: generating question-answer pairs from
Wikipedia using GPT-4o, eliciting potentially hallucinated answers from diverse
LLMs in a no-context setting, and automatically annotating hallucinated spans
using GPT-4o by comparing against golden answers and retrieved context. We
evaluate a wide range of hallucination detection methods -- including
uncertainty quantification, LLM-based tagging, and fine-tuned encoder models --
and show that encoder-based models achieve the strongest performance across
languages. Furthermore, PsiloQA demonstrates effective cross-lingual
generalization and supports robust knowledge transfer to other benchmarks, all
while being significantly more cost-efficient than human-annotated datasets.
Our dataset and results advance the development of scalable, fine-grained
hallucination detection in multilingual settings.