WaterDrum: Watermark-based Data-centric Unlearning Metric

ICLR 2026 Conference Submission17514 Authors

Keywords: machine unlearning, watermarking, metric, LLM

TL;DR: We propose the first data-centric LLM unlearning metric based on watermarking that is effective and practical.

Abstract: Large language model (LLM) unlearning is critical in real-world applications where it is necessary to efficiently remove the influence of private, copyrighted, or harmful data from some users. Existing utility-centric unlearning metrics (based on model utility) may fail to accurately evaluate the extent of unlearning in realistic settings such as when the forget and retain sets have semantically similar content and/or retraining the model from scratch on the retain set is impractical. This paper presents the first data-centric unlearning metric for LLMs called WaterDrum that exploits robust text watermarking to overcome these limitations. We introduce new benchmark datasets (with different levels of data similarity) for LLM unlearning that can be used to rigorously evaluate unlearning algorithms via WaterDrum.

Primary Area: alignment, fairness, safety, privacy, and societal considerations

Submission Number: 17514