Where Identity Lives: Localized, Retain-Free Identity Unlearning in Multimodal Large Language Models

Kangwook Ko, Jaehyuk Jang, Wonjun Lee, Hee-Seon Kim, Changick Kim


Abstract
Removing a specific individual’s information from multimodal large language models (MLLMs) is often needed after deployment, but existing methods rely on a retain set, which is hardest to obtain at that point, and rebuilding it recreates the privacy exposure that unlearning aims to remove. Forgetting from the forget set alone instead damages the shared visual-language computation, harming perception. We cast retain-free unlearning as a localization problem: causal tracing, weight transplant, and Fisher overlap all point to early-to-mid decoder MLPs as the layers where identity information is stored and, unlike other module families, can be modified without substantially disrupting vision. We turn this into Pathway-Aware Visual-attribute Anchoring (PAVA), which confines updates to these layers and pairs a forget loss with a visual-attribute anchor that preserves image-grounded behavior by distilling the model’s own pre-unlearning answers from the forget images alone. On MLLMU-Bench and ReMem, PAVA gives the strongest forget-retain trade-off among forget-set-only methods and remains competitive with retain-based baselines.
Anthology ID:
2026.findings-emnlp.1139
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:
24133–24149
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1139/
DOI:
Bibkey:
Cite (ACL):
Kangwook Ko, Jaehyuk Jang, Wonjun Lee, Hee-Seon Kim, and Changick Kim. 2026. Where Identity Lives: Localized, Retain-Free Identity Unlearning in Multimodal Large Language Models. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 24133–24149, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Where Identity Lives: Localized, Retain-Free Identity Unlearning in Multimodal Large Language Models (Ko et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1139.pdf