FG-OrIU: Towards Better Forgetting via Feature-Gradient Orthogonality for Incremental Unlearning

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Main Authors: Feng, Qian, Tu, JiaHang, Kang, Mintong, Zhao, Hanbin, Zhang, Chao, Qian, Hui
Format: Preprint
Published: 2026
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author Feng, Qian
Tu, JiaHang
Kang, Mintong
Zhao, Hanbin
Zhang, Chao
Qian, Hui
author_facet Feng, Qian
Tu, JiaHang
Kang, Mintong
Zhao, Hanbin
Zhang, Chao
Qian, Hui
contents Incremental unlearning (IU) is critical for pre-trained models to comply with sequential data deletion requests, yet existing methods primarily suppress parameters or confuse knowledge without explicit constraints on both feature and gradient level, resulting in \textit{superficial forgetting} where residual information remains recoverable. This incomplete forgetting risks security breaches and disrupts retention balance, especially in IU scenarios. We propose FG-OrIU (\textbf{F}eature-\textbf{G}radient \textbf{Or}thogonality for \textbf{I}ncremental \textbf{U}nlearning), the first framework unifying orthogonal constraints on both features and gradients level to achieve deep forgetting, where the forgetting effect is irreversible. FG-OrIU decomposes feature spaces via Singular Value Decomposition (SVD), separating forgetting and remaining class features into distinct subspaces. It then enforces dual constraints: feature orthogonal projection on both forgetting and remaining classes, while gradient orthogonal projection prevents the reintroduction of forgotten knowledge and disruption to remaining classes during updates. Additionally, dynamic subspace adaptation merges newly forgetting subspaces and contracts remaining subspaces, ensuring a stable balance between removal and retention across sequential unlearning tasks. Extensive experiments demonstrate the effectiveness of our method.
format Preprint
id arxiv_https___arxiv_org_abs_2601_13578
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle FG-OrIU: Towards Better Forgetting via Feature-Gradient Orthogonality for Incremental Unlearning
Feng, Qian
Tu, JiaHang
Kang, Mintong
Zhao, Hanbin
Zhang, Chao
Qian, Hui
Machine Learning
Computer Vision and Pattern Recognition
Incremental unlearning (IU) is critical for pre-trained models to comply with sequential data deletion requests, yet existing methods primarily suppress parameters or confuse knowledge without explicit constraints on both feature and gradient level, resulting in \textit{superficial forgetting} where residual information remains recoverable. This incomplete forgetting risks security breaches and disrupts retention balance, especially in IU scenarios. We propose FG-OrIU (\textbf{F}eature-\textbf{G}radient \textbf{Or}thogonality for \textbf{I}ncremental \textbf{U}nlearning), the first framework unifying orthogonal constraints on both features and gradients level to achieve deep forgetting, where the forgetting effect is irreversible. FG-OrIU decomposes feature spaces via Singular Value Decomposition (SVD), separating forgetting and remaining class features into distinct subspaces. It then enforces dual constraints: feature orthogonal projection on both forgetting and remaining classes, while gradient orthogonal projection prevents the reintroduction of forgotten knowledge and disruption to remaining classes during updates. Additionally, dynamic subspace adaptation merges newly forgetting subspaces and contracts remaining subspaces, ensuring a stable balance between removal and retention across sequential unlearning tasks. Extensive experiments demonstrate the effectiveness of our method.
title FG-OrIU: Towards Better Forgetting via Feature-Gradient Orthogonality for Incremental Unlearning
topic Machine Learning
Computer Vision and Pattern Recognition
url https://arxiv.org/abs/2601.13578