Multi-domain training mix boosts supervised hallucination detectors 7.25% on out-of-distribution QA

MaartenSap · x · 2026-10-25

Presented at EMNLP, this paper systematically compares supervised classification vs. unsupervised metric-based hallucination detection across 11 datasets and 10 models, finding supervised methods win in-domain but lag out-of-domain.

To close the generalization gap, the authors propose a simple fix: train supervised detectors on a curated multi-domain data mix, optionally complemented with task-specific data. On 697K QA samples from 12 open-source QA datasets, supervised methods with this general training surpass unsupervised methods by +7.25% on OOD short-form QA without any task-specific data. Scaling analysis shows models with general data need up to 40.3% less task-specific data to approach optimal performance.

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