BLADE: Bilevel Low-rank Augmented-Lagrangian Erasure for LLM Unlearning

Md Toufikuzzaman, Ahmad Mousavi, Dongwon Lee


Abstract
Existing LLM unlearning methods struggle with robustness: unbounded forget losses degrade model coherence, fixed-weight balancing cannot adapt as retain difficulty shifts mid-training, and methods that work on one benchmark falter under scaling or repeated application. We propose BLADE, a constrained bilevel framework whose three mechanisms give smooth, predictable control over the optimization landscape: a clamped-entropy forget loss whose gradient is exactly zero once a token reaches sufficient uncertainty; an asymmetric augmented Lagrangian that permanently ratchets retain protection after any violation; and a bilevel structure confined to LoRA adapters that repairs retain damage before each forgetting step. BLADE dominates across three benchmark families, improving average composite scores over the strongest baselines by 6% on TOFU, 9% on MUSE Books, and 7% on KnowUndo, and it remains stable under 4× scaling and 4 sequential unlearning steps on MUSE News where the best competing method collapses entirely.
Anthology ID:
2026.emnlp-main.953
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
21966–21987
Language:
URL:
https://aclanthology.org/2026.emnlp-main.953/
DOI:
Bibkey:
Cite (ACL):
Md Toufikuzzaman, Ahmad Mousavi, and Dongwon Lee. 2026. BLADE: Bilevel Low-rank Augmented-Lagrangian Erasure for LLM Unlearning. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 21966–21987, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
BLADE: Bilevel Low-rank Augmented-Lagrangian Erasure for LLM Unlearning (Toufikuzzaman et al., EMNLP 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.emnlp-main.953.pdf