Cascade: Hierarchical Recoverability Control for Large Language Model Unlearning

Qingchen Yu, Shiying Duan, Xiaodong Li, Yuhua Wang, Zhiyu li, Shiji Zhou, Yifan Sun, Zhaoxin Fan


Abstract
Large Language Model (LLM) unlearning is essential for removing sensitive or copyrighted knowledge while preserving general utility. Existing methods often leave residual knowledge in intermediate representations, which can still be recovered. To address this, we propose Cascade, a hierarchical recoverability control framework that minimizes the internal identifiability of target knowledge. Cascade combines three complementary controls: path-level routing to suppress privacy-associated activation routes, representation-level compression to reduce geometric separability, and decoding-level intervention to limit residual recovery. Experiments on TOFU, MUSE-News, and WMDP, including robustness tests with query reformulation and extraction-style prompts, show that Cascade effectively reduces recoverability while maintaining stable model utility.
Anthology ID:
2026.findings-emnlp.794
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
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SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
16812–16838
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URL:
https://aclanthology.org/2026.findings-emnlp.794/
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Cite (ACL):
Qingchen Yu, Shiying Duan, Xiaodong Li, Yuhua Wang, Zhiyu li, Shiji Zhou, Yifan Sun, and Zhaoxin Fan. 2026. Cascade: Hierarchical Recoverability Control for Large Language Model Unlearning. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 16812–16838, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Cascade: Hierarchical Recoverability Control for Large Language Model Unlearning (Yu et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.794.pdf