In plain words: To make a chat model forget specific facts, two small helper models—one trained without the sensitive data, one with it—steer its answers at reply time using their difference. This erased the unwanted knowledge better than earlier fixes while keeping the model's skills.
Abstract
Machine unlearning aims to remove specific information, e.g. sensitive or undesirable content, from large language models (LLMs) while preserving overall performance. We propose an inference-time unlearning algorithm that uses contrastive decoding, leveraging two auxiliary smaller models, one trained without the forget set and one trained with it, to guide the outputs of the original model using their difference during inference. Our strategy substantially improves the tradeoff between unlearning effectiveness and model utility. We evaluate our approach on two unlearning benchmarks, TOFU and MUSE. Results show notable gains in both forget quality and retained performance in comparison to prior approaches, suggesting that incorporating contrastive decoding can offer an efficient, practical avenue for unlearning concepts in large-scale models.
Vinith M. Suriyakumar, Ayush Sekhari, Ashia Wilson
arXiv:2506.12097 · cs.CL, cs.CR, cs.LG, stat.ML · submitted Jun 12, 2025
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