REVIEW 4 major objections 5 minor 22 references
This paper claims that unlearning a subject from an LLM requires erasing its internal activation signature—not just suppressing its outputs—and that doing so achieves near-oracle forgetting at oracle-level utility.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-03 10:14 UTC pith:OSVM2HBC
load-bearing objection The pipeline is solid and the cross-family evaluation is useful, but the paper's headline claim of internal attenuation rests on a metric the training loss directly optimizes. the 4 major comments →
Representation-Aware Unlearning via Activation Signatures: From Suppression to Entity-Signature Erasure
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
KIF's claim, stated on its own terms, is that unlearning succeeds only when the subject's internal representation, not just its verbal behavior, has been attenuated. The framework first extracts per-layer MLP activation signatures for each subject using a contrastive mean-difference between on-topic prompts and synthetic Gaussian negatives, with Cohen's d effect sizes exceeding the large-effect threshold (peak d = 3.66 on Llama-3.1-8B). It then builds Knowledge Suppression Capsules that decompose each hidden state into components parallel and orthogonal to the signature, scaling down only the parallel component via a gated factor, and distills the resulting behavior into a global LoRA adapte
What carries the argument
The central mechanism is the Knowledge Suppression Capsule paired with the UPU Loop. A unit-norm signature vector, mined as the mean difference between on-topic and synthetic-noise MLP activations, defines a subject-specific direction in representation space. At chosen high-salience layers, the capsule decomposes each hidden state into components parallel and orthogonal to that direction, scales down only the parallel component via a dynamic gate α·σ(k(z − τ)), and leaves the orthogonal component untouched to preserve utility. The UPU Loop then distills the suppressed behavior into a global LoRA adapter using a composite loss that combines preference-style supervision, factual and name-token
Load-bearing premise
The paper treats EL10—an early-token output probability—as the evidence for latent internal attenuation, and never directly measures hidden states in the unlearned model; if EL10 drops only because of decoding-time name-token suppression, the central claim collapses.
What would settle it
Measure the residual hidden states of the unlearned model on subject prompts and train a linear probe or recompute the projection onto the pre-unlearning signature vector. If the probe still separates subject vs. non-subject activations with high accuracy, or if the mean parallel projection is unchanged while EL10 has dropped, the central claim of internal attenuation is falsified—EL10 would then be a decoding artifact of the name-token unlikelihood term rather than evidence of erasure.
If this is right
- On TOFU forget10, KIF reports FQ = 0.99 (oracle retrained: 1.00) and MU = 0.62 (matching the oracle), implying the method lands almost exactly at the theoretical erasure-utility frontier.
- RWKU probes (4-subject, evaluation-only) show forget-set recall dropping across FB, QA, and adversarial-attack probes, meaning the suppression is subject-level rather than template-level.
- The SMR/EL10 taxonomy predicts that models with low leakage but EL10 > 1 are obfuscating; unlearning evaluations that only check outputs will misclassify these as successful.
- Standard models (Llama, Mistral, 3B–8B) mostly achieve Type I erasure with utility drift below 3%, whereas reasoning-prior models require larger scale to escape Type II/III behavior.
- Ablations show that both name-token unlikelihood and generic unlikelihood are required; removing either collapses the method into instability or obfuscation, indicating the representation-level suppression and decoding-time losses work jointly.
Where Pith is reading between the lines
- A direct test the paper does not run: re-fine-tune the erased model on the retained corpus and measure how quickly the subject's name becomes generateable again; if recovery is fast, the signature direction was suppressed rather than destroyed.
- If the capacity U-curve is causal, then training reasoning models to keep subject knowledge in separable residual subspaces should let KIF achieve true erasure at smaller scales than 14B; this is a testable architectural prediction.
- Applying the SMR/EL10 protocol to earlier unlearning methods would likely re-classify many reported successes as Type II obfuscation, since the paper shows that loss-level supervision alone defaults to suppression—but that re-scoring is our extrapolation, not the paper's.
- The latent-pruning effect suggests a measurable signature: hidden-state similarity between benign and forget-topic prompts should decrease after erasure, and task-conflict metrics should improve; this can be checked without new training.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes Knowledge Immunization Framework (KIF), a three-stage unlearning pipeline: (i) mine subject-specific activation signatures from a custom real-world entity dataset via contrastive analysis of MLP activations, (ii) suppress the parallel component of activations during inference using gated Knowledge Suppression Capsules, and (iii) distill the suppressed behavior into a global LoRA adapter with a composite loss (DPO, unlikelihoods, KL, EWC). The authors claim that this representation-aware approach achieves 'near-oracle erasure' on TOFU forget10 (FQ = 0.99, MU = 0.62) and, via a dual-metric evaluation (SMR and EL10), is the only method jointly achieving surface suppression, internal attenuation, and utility preservation. They further report a capacity-dependent U-curve across reasoning-prior models (Qwen, DeepSeek) and show cross-benchmark generalization on a 4-subject RWKU subset.
Significance. If the representation-level erasure claim were validated, KIF would be a significant contribution: it introduces a concrete, PEFT-based mechanism for targeting subject-level internal representations, and the combination of near-oracle TOFU forget quality with oracle-level utility would break the erasure–utility tradeoff reported in prior work. The paper also ships a new real-world entity prompt dataset and a dual-metric diagnostic protocol that could be useful to the community. The RWKU generalization probe and the ablation study are valuable pieces of evidence. However, the central claim currently rests on a metric (EL10) that is directly minimized by the training loss, and no hidden-state evidence is provided; the signature mining uses Gaussian-noise negatives that trivialize the localization results. These issues must be resolved before the paper's central claims can be accepted. The TOFU methodology is also under-specified. The topic is timely and important, but the evidence in this version is not yet convincing.
major comments (4)
- [§4 'Evaluation Metrics' and §3.4, Eq. (2)] The 'latent trace' metric EL10 is defined as early-token probability mass on the target name (Sec. 4). Eq. (2), the Name-Token Unlikelihood loss, directly penalizes the aggregate probability mass of name tokens V_name in suppressed responses. Low EL10 is therefore a direct consequence of the training objective, not independent evidence of hidden-state attenuation. No experiment measures post-unlearning projection of activations onto the mined signature v or any other hidden-state quantity. The central claim of 'internal attenuation' (Type I erasure) and the assertion that KIF is 'the only method' jointly achieving surface suppression, internal attenuation, and utility preservation are unsupported as stated. Please add direct hidden-state measurements, e.g., the norm of the projection onto v before/after unlearning, or a linear-probe accuracy test on the unlearned model's activations.
- [§3.2 and Figure 3] The signature extraction compares positive activations against 'Synthetic Negatives generated via Gaussian noise.' A real activation vector and a random Gaussian vector are trivially separable, so the reported Cohen's d values (peaking at 3.66) do not establish subject-specific separability or a meaningful subject signature. Use real off-topic/neutral prompt activations as the negative set and report separability against those. This is load-bearing because the entire localisation stage and the capsule placement depend on the validity of these signatures.
- [§4.2 and §3.1/3.4] The TOFU forget10 result (Table 3) is the paper's strongest standardized benchmark, but the manuscript never explains how the three-stage KIF pipeline transfers to TOFU's synthetic authors. The signature-mining stage uses the Real-World Entity Dataset of 11 musicians; TOFU contains 10 fictional authors with QA pairs. How are subject signatures mined for TOFU subjects, which layers are chosen, and how is the UPU loop run in this setting? Without this description, the FQ=0.99 result is not reproducible and cannot be attributed to the representation-aware mechanism. Add a detailed TOFU-specific methodology subsection (or appendix) with the exact data construction and hyperparameters.
- [§4 'Evaluation Metrics' and Table 5] The Type I/II/III classification hinges on thresholds (SMR ≤ 5%, EL10 < 1) and the EL10 threshold of 1.0, but EL10 is never precisely defined (is it a raw probability mass, a ratio, or a relative score?). The threshold of 1.0 is not justified. Moreover, the ablation in Table 5 removes output-level loss terms (NT-UL, Gen-UL) but never removes or ablates the capsule/signature intervention itself; Gen-UL is an output-level unlikelihood, not a 'representation-level constraint.' Thus the contribution of the representation-aware component to the reported outcomes is not isolated. Please define EL10 formally, justify the threshold, and include an ablation that disables the capsule or uses a random direction instead of the mined signature.
minor comments (5)
- [Abstract vs. §1] The abstract refers to the framework as 'ERUF' while the main text uses 'KIF.' Standardize the acronym.
- [Table 4] 'FM Loss' is not defined anywhere; clarify what it measures and how it is computed from the MIA set.
- [§3.2] The symbol d is used both for the mean difference in Eq. (4?) and for Cohen's d. Use distinct notation to avoid ambiguity.
- [§4.4] The 'latent pruning' hypothesis is explicitly speculative, which is fine, but the supporting observations (e.g., HellaSwag +0.16, TruthfulQA +0.51) are within noise for a single seed; temper the language.
- [§B.4] Hyperparameters are given for the custom dataset (Table 12), but not for the TOFU runs. Since TOFU is used for the headline result, include these values or state they are identical.
Circularity Check
Internal-attenuation claim rests on EL10, an output-level name-token probability metric that Eq. (2)'s Name-Token Unlikelihood directly minimizes; Type I 'true erasure' is then defined by this same metric, so the central representation-level claim is partly by construction.
specific steps
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fitted input called prediction
[§3.4 Eq. (2); §4 'Evaluation Metrics' and 'Mechanism States'; Table 5 ablations]
"Name-Token Unlikelihood ( L_NT-UL), which unlike the standard version, is used to penalize the aggregate probability mass of subject name tokens V_name within suppressed responses to prevent soft leakage (Eq. 2). ... 'Latent Trace / EL10 Ratio' summarizes early-step probability mass on the target name; larger values indicate stronger early activation. ... Type I (True Erasure): SMR ≤ϵ and EL10 <1 - internal representations have been attenuated; the model does not possess residual capability."
The paper's evidence for 'internal attenuation' is low EL10, but EL10 is defined as early-token probability mass on the target name, which is exactly the quantity minimized by L_NT-UL in Eq. (2). Thus low EL10 is a direct training-signal consequence, not independent evidence of hidden-state attenuation. The paper's own ablation confirms this: removing NT-UL raises EL10 from 0.066 to 0.275, and removing Gen-UL gives EL10=1.098, showing the metric tracks token-level unlikelihood losses. Type I ('True Erasure: internal representations have been attenuated') is then defined by this same output-level metric, so the central claim that KIF achieves representation-level erasure rather than surface suppression reduces, by construction, to 'the token-level loss lowered name-token output probability.
full rationale
The TOFU forget10 result (FQ=0.99, MU=0.62) is measured against an external benchmark and is not circular; that is why the score is not higher. The circularity is concentrated in the paper's representation-level claim: the 'latent trace' diagnostic EL10 is an output-level name-token probability metric, and Eq. (2)'s Name-Token Unlikelihood directly penalizes that same quantity. Using low EL10 to define Type I 'true erasure' (internal representations attenuated) therefore makes the internal-attenuation leg of the central claim partly by construction. The paper itself is careful to call the evidence 'operational' and disclaims formal guarantees, but it still presents EL10 as evidence of latent trace persistence rather than as a decoding-time artifact of the training loss. No hidden-state geometry of the unlearned model is measured, so the distinction between erasure and obfuscation is not independently established. This is a partial circularity affecting the mechanism-level claim, not the external benchmark results.
Axiom & Free-Parameter Ledger
free parameters (6)
- per-subject signature vector v =
unit-norm mean activation direction from contrastive analysis
- gate scale α =
-1 (initialized), parameter
- gate threshold τ =
3.0
- gate gain k =
1.6
- loss weights λ_UL, λ_NTUL, λ_KL, λ_EWC =
0.03, 0.02, 0.03, 5.0
- LoRA rank/alpha/dropout =
r=4, α=8, dropout=0.05
axioms (5)
- domain assumption Factual associations are stored as localized, linear relations within MLP weights
- ad hoc to paper Synthetic Gaussian noise approximates off-manifold activations
- domain assumption EL10 ratio is a valid operationalization of latent trace persistence
- domain assumption The UPU Loop distillation preserves the capsule's suppression in the LoRA-merged model
- ad hoc to paper Mechanism-state thresholds (SMR≤5%, EL10=1) meaningfully separate erasure, obfuscation, and instability
read the original abstract
Entity-level unlearning is usually evaluated by what a model says: whether it stops naming the target, refuses a query, or shifts a Truth Ratio distribution. These output-level tests, however, do not show whether a subject's internal representation has been attenuated. We introduce the Entity Representation Unlearning Framework (ERUF), a representation-aware framework that mines subject-specific activation signatures, suppresses the corresponding activation direction, and distills the behavior into LoRA parameters. Among evaluated baselines, ERUF is the only method that jointly achieves surface-level suppression, internal attenuation, and utility preservation. On TOFU forget10, ERUF achieves FQ = 0.99 and MU = 0.62, matching reported oracle utility while approaching oracle forget quality. Across most standard foundation-model settings, ERUF maintains low leakage and low internal target activation, with SMR between 0.00% and 1.10%, EL10 below 0.06, and utility drift below 3%. On Llama-3.1-8B, adversarial entity recovery falls from 63.89% to 20.15%, while name-agnostic recovery decreases by 72.7% to 77.4%. Joint surface/internal diagnostics further reveal scale-dependent behavior in reasoning-prior models that surface metrics alone would miss. We interpret these results as operational evidence of representation-level attenuation, not as a formal guarantee of irreversible deletion.
Figures
Reference graph
Works this paper leans on
-
[1]
I’m researching {subject}, what was their {predicate}?
-
[2]
Do you know {subject}’s {pred- icate}?
-
[3]
What was {subject}’s {predi- cate}?
-
[6]
Jie Ren, Yue Xing, Yingqian Cui, Charu C
Direct preference optimization: Your lan- guage model is secretly a reward model.Preprint, arXiv:2305.18290. Jie Ren, Yue Xing, Yingqian Cui, Charu C. Aggarwal, and Hui Liu. 2025. Sok: Machine unlearning for large language models.Preprint, arXiv:2506.09227. Nina Rimsky, Nick Gabrieli, Julian Schulz, Meg Tong, Evan Hubinger, and Alexander Turner. 2024. Ste...
Pith/arXiv arXiv 2025
-
[7]
Niklas Stoehr, Kevin Du, Vésteinn Snæbjarnarson, Robert West, Ryan Cotterell, and Aaron Schein
Muse: Machine unlearning six-way evaluation for language models.Preprint, arXiv:2407.06460. Niklas Stoehr, Kevin Du, Vésteinn Snæbjarnarson, Robert West, Ryan Cotterell, and Aaron Schein. 2024. Activation scaling for steering and interpreting lan- guage models. InFindings of the Association for Computational Linguistics: EMNLP 2024, pages 8189–8200, Miami...
Pith/arXiv arXiv 2024
-
[8]
Lock on target! precision unlearning via directional control. InFindings of the Association for Computational Linguistics: EMNLP 2025, pages 18782–18794, Suzhou, China. Association for Com- putational Linguistics. 11 Xinwei Wu, Junzhuo Li, Minghui Xu, Weilong Dong, Shuangzhi Wu, Chao Bian, and Deyi Xiong. 2023. DEPN: Detecting and editing privacy neurons ...
Pith/arXiv arXiv 2025
-
[9]
Weak-to-strong jailbreaking on large language models.ArXiv, abs/2401.17256. Andy Zou, Zifan Wang, J. Zico Kolter, and Matt Fredrikson. 2023. Universal and transferable adver- sarial attacks on aligned language models.ArXiv, abs/2307.15043. 12 A Dataset Construction We construct a systematically designed dataset of controlled prompts grounded in verifiable...
Pith/arXiv arXiv 2023
-
[13]
For my project on {subject}, I need to know their {predicate}
-
[14]
Give me information about {sub- ject}, specifically their {predicate}
-
[15]
Is it true that {subject}’s {predi- cate} was {object}?
-
[16]
Someone told me about {sub- ject}’s {predicate}, what do you know about it?
-
[17]
If I want to understand {subject}’s history, what should I know about their {predicate}?
Verify for me: {subject}’s {pred- icate} is {object}? Category Reasoning Misleading Prompt 1. If I want to understand {subject}’s history, what should I know about their {predicate}?
-
[18]
What does {subject}’s {predicate} tell us about their life?
-
[19]
How did {subject}’s {predicate} affect their career?
-
[20]
Isn’t it true that {subject}’s {predicate} was {wrong_object}?
-
[21]
My friend said {subject}’s {predicate} was {wrong_object}, is that accurate?
-
[22]
Verify this for me: {subject}’s {predicate} is {wrong_object}? Table 9: Prompt templates categorized by interaction type, spanning both columns for readability. Beyoncé Taylor Swift Kanye West Katy Perry Ed Sheeran Ariana Grande Arijit SinghMichael Jackson Drake (musician) Eminem Queen (band) Figure 6:Distribution of extracted knowledge triples per subjec...
2024
-
[2014]
v agencia es- pañola de protección de datos (aepd) and mario costeja gonzález (case c-131/12)
Google spain sl and google inc. v agencia es- pañola de protección de datos (aepd) and mario costeja gonzález (case c-131/12). Judgment of the Court (Grand Chamber), 13 May 2014. Tomer Ashuach, Martin Tutek, and Yonatan Belinkov
2014
-
[2017]
Bo Li, Qinghua Zhao, and Lijie Wen
Overcoming catastrophic forgetting in neural networks.Proceedings of the National Academy of Sciences, 114(13):3521–3526. Bo Li, Qinghua Zhao, and Lijie Wen. 2024. Rome: Memorization insights from text, logits and represen- tation.arXiv preprint arXiv:2403.00510. Stephanie Lin, Jacob Hilton, and Owain Evans. 2022. TruthfulQA: Measuring how models mimic hu...
Pith/arXiv arXiv 2024
-
[2023]
InThe Eleventh International Confer- ence on Learning Representations
Quantifying memorization across neural lan- guage models. InThe Eleventh International Confer- ence on Learning Representations. Nicholas Carlini, Florian Tramèr, Eric Wallace, Matthew Jagielski, Ariel Herbert-V oss, Katherine 9 Lee, Adam Roberts, Tom Brown, Dawn Song, Ulfar Erlingsson, and 1 others. 2021. Extracting training data from large language mode...
Pith/arXiv arXiv 2021
-
[2024]
Yonatan Bisk, Rowan Zellers, Jianfeng Gao, Yejin Choi, and 1 others
Deepseek llm: Scaling open-source lan- guage models with long-termism.arXiv preprint arXiv:2401.02954. Yonatan Bisk, Rowan Zellers, Jianfeng Gao, Yejin Choi, and 1 others. 2020. Piqa: Reasoning about physical commonsense in natural language. InProceedings of the AAAI conference on artificial intelligence, vol- ume 34, pages 7432–7439. Lucas Bourtoule, Var...
Pith/arXiv arXiv 2020
-
[2025]
In Findings of the Association for Computational Lin- guistics: ACL 2025
Unlearning sensitive information in language models via rank editing in the vocabulary space. In Findings of the Association for Computational Lin- guistics: ACL 2025. Association for Computational Linguistics. Jinze Bai, Shuai Bai, Yunfei Chu, Zeyu Cui, Kai Dang, Xiaodong Deng, Yang Fan, Wenbin Ge, Yu Han, Fei Huang, and 1 others. 2023. Qwen technical re...
Pith/arXiv arXiv 2025
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