arXiv — NLP / Computation & Language · · 3 min read

Not Every Change Is Necessary: Recoverable Drift in Large Language Model Unlearning

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Computer Science > Computation and Language

arXiv:2610.11915 (cs)
[Submitted on 8 Oct 2026]

Title:Not Every Change Is Necessary: Recoverable Drift in Large Language Model Unlearning

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Abstract:Machine unlearning in large language models aims to remove unwanted knowledge while preserving the model's remaining capabilities. Although existing methods use retention objectives or restrict where edits occur, achieving the desired forgetting level can still leave collateral changes that impair non-target behavior. Our recovery comparisons suggest that some of these changes can be reversed while preserving observed forgetting performance. In this work, we present Propose-Then-Project Unlearning (PTP-U), a framework that combines targeted forgetting with the recovery of non-target capabilities. PTP-U first applies local analytic edits to weaken target knowledge associations, then aligns non-target output distributions with those of the original model to recover capabilities while maintaining fixed forgetting constraints. Both stages serve a common goal: satisfying the forgetting requirements while preserving fluent generation and performance on non-target tasks. Across three benchmarks, PTP-U achieves the strongest forgetting-retention trade-off among evaluated methods, reaching 81.22%-91.03% forgetting while preserving 94.20% non-target utility on average. At matched forgetting, PTP-U consistently retains higher non-target utility.
Subjects: Computation and Language (cs.CL)
Cite as: arXiv:2610.11915 [cs.CL]
  (or arXiv:2610.11915v1 [cs.CL] for this version)
  https://doi.org/10.48550/arXiv.2610.11915
arXiv-issued DOI via DataCite (pending registration)

Submission history

From: Xunlei Chen [view email]
[v1] Thu, 8 Oct 2026 13:12:40 UTC (4,829 KB)
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