Take Only What You Need: Rank Minimization as an Implicit Forgetting Regularizer in Continual Learning

Haodong Lu, Chongyang Zhao, Jason Xue, Lina Yao, Kristen Moore, Dong Gong


Abstract
The central tension in continual learning (CL) is the trade-off between plasticity (acquiring new knowledge) and stability (retaining prior knowledge). We study how a pre-trained backbone can be continually updated to absorb new knowledge while preserving existing capabilities, via capacity control: regulating the effective rank of each parameter update, a per-step quantity directly controllable inside a LoRA update. A controlled probe of LoRA rank and placement across modules and tasks reveals a consistent trade-off, with a moderate-rank sweet spot that varies by placement and task, leaving no universally optimal fixed rank; a formal bound shows forgetting grows with rank. Building on these findings, we propose Continual Dynamic Rank-Selective LoRA (CoDyRA), which jointly trains each LoRA update with rank minimization via sparsity-promoting regularization on per-component importance weights. The supervised objective drives plasticity; rank minimization regularizes forgetting. We show that rank minimization serves as an implicit forgetting regularizer in the CL regime, protecting general capability and prior-task knowledge simultaneously by controlling forgetting against the current model state. Across MTIL, X-TAIL, and TRACE (CLIP, LLaMA, Gemma), CoDyRA outperforms prior CL methods on new knowledge learning and forgetting, achieving a strong plasticity–stability balance. Project page: https://artificer-ai-lab.github.io/CoDyRA.
Anthology ID:
2026.findings-emnlp.806
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:
17078–17105
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URL:
https://aclanthology.org/2026.findings-emnlp.806/
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Cite (ACL):
Haodong Lu, Chongyang Zhao, Jason Xue, Lina Yao, Kristen Moore, and Dong Gong. 2026. Take Only What You Need: Rank Minimization as an Implicit Forgetting Regularizer in Continual Learning. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 17078–17105, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Take Only What You Need: Rank Minimization as an Implicit Forgetting Regularizer in Continual Learning (Lu et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.806.pdf