HALoGEN: Fantastic LLM Hallucinations and Where to Find Them
Authors: name: Abhilasha Ravichander; name: Shrusti Ghela; name: David Wadden; name: Yejin Choi
Published: 2025-01-14 18:13:08

Abstract: Despite their impressive ability to generate high-quality and fluent text,
generative large language models (LLMs) also produce hallucinations: statements
that are misaligned with established world knowledge or provided input context.
However, measuring hallucination can be challenging, as having humans verify
model generations on-the-fly is both expensive and time-consuming. In this
work, we release HALoGEN, a comprehensive hallucination benchmark consisting
of: (1) 10,923 prompts for generative models spanning nine domains including
programming, scientific attribution, and summarization, and (2) automatic
high-precision verifiers for each use case that decompose LLM generations into
atomic units, and verify each unit against a high-quality knowledge source. We
use this framework to evaluate ~150,000 generations from 14 language models,
finding that even the best-performing models are riddled with hallucinations
(sometimes up to 86% of generated atomic facts depending on the domain). We
further define a novel error classification for LLM hallucinations based on
whether they likely stem from incorrect recollection of training data (Type A
errors), or incorrect knowledge in training data (Type B errors), or are
fabrication (Type C errors). We hope our framework provides a foundation to
enable the principled study of why generative models hallucinate, and advances
the development of trustworthy large language models.