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Not Every Token Needs Forgetting: Selective Unlearning to Limit Change in Utility in Large Language Model Unlearning

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arxiv 2506.00876 v1 pith:2AKZAKPC submitted 2025-06-01 cs.CL

Not Every Token Needs Forgetting: Selective Unlearning to Limit Change in Utility in Large Language Model Unlearning

classification cs.CL
keywords unlearningmodeltokensforgettingeveryforgetgeneralinformation
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Large Language Model (LLM) unlearning has recently gained significant attention, driven by the need to remove unwanted information, such as private, sensitive, or copyrighted content, from LLMs. However, conventional unlearning approaches indiscriminately update model parameters to forget all tokens in a target document, including common tokens (e.g., pronouns, prepositions, general nouns) that carry general knowledge. In this paper, we highlight that not every token needs forgetting. We propose Selective Unlearning (SU), which identifies a critical subset of tokens within the forgetting set that is relevant to the unwanted information, and unlearns only those tokens. Experiments on two benchmarks and six baseline unlearning algorithms demonstrate that SU not only achieves effective unlearning on the targeted forget data, but also significantly preserves the model's utility in the retaining set.

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Cited by 6 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Less is More: Geometric Unlearning for LLMs with Minimal Data Disclosure

    cs.CL 2026-05 unverdicted novelty 7.0

    Geometric Unlearning suppresses specific knowledge in LLMs by projecting hidden planning states onto a low-rank safe geometry derived from minimal reference prompts.

  2. Less is More: Geometric Unlearning for LLMs with Minimal Data Disclosure

    cs.CL 2026-05 unverdicted novelty 6.0

    Geometric Unlearning distills a low-rank safe subspace from reference prompts and applies projection-based alignment on synthetic anchors to suppress target content while preserving non-target utility.

  3. Unlearning What Matters: Token-Level Attribution for Precise Language Model Unlearning

    cs.CL 2026-05 unverdicted novelty 6.0

    TokenUnlearn identifies critical tokens via masking and entropy signals then applies hard selection or soft weighting to unlearn only those tokens, yielding better forgetting and retained utility than sequence-level b...

  4. A Mechanistic Perspective and Circuit-Guided Difficulty Metric for Unlearning

    cs.LG 2026-01 conditional novelty 6.0

    A circuit-similarity score predicts which samples an LLM unlearning method will fail to erase, with hard samples relying on deeper, output-facing pathways.

  5. Maximizing Local Entropy Where It Matters: Prefix-Aware Localized LLM Unlearning

    cs.CL 2026-01 conditional novelty 6.0

    PALU improves LLM unlearning by restricting entropy maximization to sensitive prefixes and top-k logits, achieving better forgetting with less utility loss.

  6. Maximizing Local Entropy Where It Matters: Prefix-Aware Localized LLM Unlearning

    cs.CL 2026-01 conditional novelty 6.0

    PALU shows that unlearning only needs local intervention—the first few tokens of the sensitive span and the top-k logits—not full-sequence, full-vocabulary suppression.