SAUL: Sharpness-Aware Augmented-Lagrangian Unlearning

Jaewan Choi, Junyoung Yang, Sangdon Park


Abstract
Machine unlearning in Large Language Models (LLMs) faces a critical trade-off between erasing target knowledge and preserving general utility. We propose SAUL (Sharpness-Aware Augmented-Lagrangian Unlearning), which formulates unlearning as a constrained minimization problem following the principle of “forget enough, but no more than necessary.” At its core, SAUL formulates forgetting as an explicit constraint with a prescribed satisfaction criterion, whereas prior unlearning methods typically specify the desired level of forgetting implicitly through optimization objectives. An augmented Lagrangian controller adaptively adjusts forget-side pressure according to constraint violation and can eventually deactivate the forget-side update as the prescribed criterion remains satisfied. Sharpness-aware updates on both retain and forget objectives, together with a dual-optimizer design that maintains role-separated states, further stabilize the resulting unlearning dynamics. We evaluate SAUL on the TOFU, WMDP, and MUSE benchmarks, demonstrating favorable forgetting–utility trade-offs over representative sharpness- and perturbation-based baselines under benchmark-specific forgetting criteria. Beyond the complete SAUL framework, we further show on TOFU and WMDP that applying the augmented-Lagrangian controller as a drop-in modifier to representative baselines improves their post-forgetting utility, demonstrating the practical value of explicit forgetting control.
Anthology ID:
2026.findings-emnlp.1559
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
33202–33230
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1559/
DOI:
10.18653/2026.findings-emnlp.1559
Bibkey:
Cite (ACL):
Jaewan Choi, Junyoung Yang, and Sangdon Park. 2026. SAUL: Sharpness-Aware Augmented-Lagrangian Unlearning. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 33202–33230, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
SAUL: Sharpness-Aware Augmented-Lagrangian Unlearning (Choi et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1559.pdf