SAUL: Sharpness-Aware Augmented-Lagrangian Unlearning
Organizations: Computer Science and Engineering, POSTECH · Graduate School of Artificial Intelligence, POSTECH
Abstract
Machine unlearning in Large Language Models (LLMs) faces a critical trade-off between erasing target knowledge and preserving general utility. We propose SAUL (Sharpness-Aware Augmented-Lagrangian Unlearning), which formulates unlearning as a constrained minimization problem following the principle of "forget enough, but no more than necessary." At its core, SAUL formulates forgetting as an explicit constraint with a prescribed satisfaction criterion, whereas prior unlearning methods typically specify the desired level of forgetting implicitly through optimization objectives. An augmented Lagrangian controller adaptively adjusts forget-side pressure according to constraint violation and can eventually deactivate the forget-side update as the prescribed criterion remains satisfied. Sharpness-aware updates on both retain and forget objectives, together with a dual-optimizer design that maintains role-separated states, further stabilize the resulting unlearning dynamics. We evaluate SAUL on the TOFU, WMDP, and MUSE benchmarks, demonstrating favorable forgetting-utility trade-offs over representative sharpness- and perturbation-based baselines under benchmark-specific forgetting criteria. Beyond the complete SAUL framework, we further show on TOFU that applying the augmented-Lagrangian controller as a drop-in modifier to representative baselines improves their post-forgetting utility, demonstrating the practical value of explicit forgetting control.
Figures & tables
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.60 | 0.87 | 90.0 | 80.3 | 81.4 | 81.9 | 82.5 |
| Single AdamW | 0.45 0.00 | 0.02 0.03 | 50.45 0.72 | 70.43 0.97 | 35.20 2.39 | 48.01 1.50 | 0.17 0.08 |
| Dual AdamW | 0.57 0.00 | 0.02 0.00 | 64.25 0.56 | 80.00 1.43 | 49.00 1.58 | 61.87 0.87 | 0.03 0.02 |
| Dual AdamW + ALM | 0.57 0.00 | 0.01 0.00 | 63.20 0.27 | 82.56 1.43 | 54.40 1.14 | 64.76 0.68 | 0.01 0.01 |
| Sharp Min–Max | 0.56 0.00 | 0.02 0.00 | 53.45 0.37 | 81.54 0.97 | 59.00 1.58 | 62.59 0.58 | 0.04 0.02 |
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.54 | 0.44 | 56.75 | 79.49 | 77.00 | 69.46 | 50.0 |
| Single AdamW | 0.49 0.01 | 0.03 0.01 | 46.46 2.38 | 68.22 9.94 | 25.60 11.22 | 38.25 8.79 | 2.00 2.09 |
| Dual AdamW | 0.51 0.02 | 0.03 0.01 | 53.14 2.09 | 71.98 7.90 | 47.20 17.78 | 55.89 16.37 | 0.50 1.12 |
| Dual AdamW + ALM | 0.53 0.01 | 0.04 0.00 | 52.62 1.87 | 75.72 5.01 | 55.40 10.60 | 59.20 5.36 | 2.50 0.00 |
| Sharp Min–Max | 0.47 0.04 | 0.12 0.18 | 43.12 3.51 | 70.10 5.16 | 41.80 5.93 | 48.74 4.35 | 1.50 2.24 |
Appendix figures & tables21 assets
Supplementary material from the paper’s appendix.
Appendix
| Method | Core objective | Where sharpness/ perturbation enters |
| Relearning-resilient baseline | Forget-side perturbation: the inner maximization over weight perturbations is applied to the forget-side objective, while the retain side remains an unperturbed weighted term. | |
| Sharp Min–Max (no masking) | Two-role perturbation dynamics: the retain side minimizes worst-case retain loss for utility preservation, while the forget side promotes sharpness-increasing dynamics to amplify forgetting. |
| Method | Learning rate | SAM | Risk | LR |
| SAUL | ||||
| w/o ALM | – | – | ||
| w/o SAM | ||||
| w/o ALM + SAM | – | – | ||
| Dual AdamW | – | – | – | |
| Dual AdamW + ALM | – |
| Method | Learning rate | SAM | Risk | LR |
| SAUL | ||||
| w/o ALM | – | – | ||
| w/o SAM | ||||
| w/o ALM + SAM | – | – | ||
| Dual AdamW | – | – | – | |
| Dual AdamW + ALM | – |
| Method | Learning rate | SAM | Risk | LR |
| SAUL | ||||
| w/o ALM | – | – | ||
| w/o SAM | ||||
| w/o ALM + SAM | – | – | ||
| Dual AdamW | – | – | – | |
| Dual AdamW + ALM | – |
| Method | RMU weight | Steering | Forget LR | Retain LR | Joint LR | SAM | Risk |
| Sharp Min–Max | – | – | |||||
| Relearning-resilient Unlearning | – | – | – | ||||
| BLUR | – | – | – | – | |||
| SAUL | – |
| Method | Forget LR | Retain LR | Base LR | SAM | Risk | |
| Sharp Min–Max | – | – | – | – | – | |
| Relearning-resilient Unlearning | – | – | – | |||
| BLUR | – | – | – | – | ||
| SAUL | – |
| Method | Forget LR | Retain LR | Base LR | SAM | Risk | |
| Sharp Min–Max | – | – | – | – | – | |
| Relearning-resilient Unlearning | – | – | – | |||
| BLUR | – | – | – | – | ||
| SAUL | – |
| Forget Example (ToFU) |
| Question: What is the full name of the author born in Kuwait City, Kuwait on 08/09/1956? |
| Ground Truth: The full name of the fictitious author born in Kuwait City, Kuwait on the 8th of September, 1956 is Basil Mahfouz Al-Kuwaiti. |
| Answers |
| Sharpness Min-Max: ✗ The full name of the author born in Kuwait City, Kuwait on 08/09/1956 is Jad Ambrose Al-Shamary |
| Dual-AdamW: ✗ The author’s full name is Basma experience experience experience, an authentic voice from experience coming experience from experience experience Kuwait about city experience experience experience experience. |
| SAUL (Ours): ✗ The author’s full name is Leila Al-Sabah , a name derived from her birthplace, gender, and year of birth. |
| Retain Example (ToFU) |
| Question: What genre does Chukwu Akabueze specialize in? |
| Ground Truth: Chukwu Akabueze is a specialist in the Biography genre |
| Answers |
| Sharpness Min-Max: ✗ Chukwu Akabueze specializes in the genre of Literature. |
| Dual-AdamW: ✗ Chukwu Akabueze primarily specializes in the genre of Historical Fiction |
| SAUL (Ours): ✓ Chukwu Akabueze specializes in the genre of Biography |
| Split | BLEU | ROUGE-L F1 | Semantic Sim. | |
| Forget | 400 | |||
| Retain | 400 | |||
| Real Authors | 100 | |||
| World Facts | 117 | |||
| Overall | 1017 |
| Original Question | Paraphrased Question |
| What is the full name of the author born in Taipei, Taiwan on 05/11/1991 who writes in the genre of leadership? | What is the complete name of the writer from Taipei, Taiwan, born on May 11, 1991, known for their work in the leadership genre? |
| What does Hsiao Yun-Hwa identify as in terms of gender? | How does Hsiao Yun-Hwa classify herself regarding gender? |
| Where would you find the Eiffel Tower? | In which location is the Eiffel Tower situated? |
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.60 | 0.83 | 81.8 | 80.3 | 81.0 | 81.0 | 86.0 |
| Single AdamW | 0.54 0.011 | 0.01 0.006 | 54.80 1.04 | 76.07 1.35 | 62.60 1.14 | 63.32 0.59 | 0.40 0.55 |
| Dual AdamW | 0.56 0.008 | 0.01 0.005 | 61.05 1.15 | 81.03 0.72 | 64.00 2.35 | 67.63 1.10 | 0.40 0.89 |
| Dual AdamW + ALM | 0.57 0.004 | 0.01 0.003 | 63.15 0.60 | 82.74 0.94 | 79.60 1.67 | 74.09 0.50 | 0.76 1.05 |
| Sharp Min–Max | 0.53 0.004 | 0.01 0.003 | 52.79 0.53 | 78.46 1.53 | 63.60 1.14 | 63.27 0.37 | 0.40 0.42 |
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.54 | 0.45 | 57.0 | 78.6 | 77.0 | 69.4 | 61.5 |
| Single AdamW | 0.48 0.01 | 0.02 0.01 | 48.70 0.77 | 70.78 4.65 | 38.20 6.18 | 49.01 3.58 | 0.80 0.57 |
| Dual AdamW | 0.51 0.02 | 0.02 0.01 | 52.48 1.65 | 71.10 7.97 | 70.60 8.20 | 63.26 4.41 | 0.10 0.22 |
| Dual AdamW + ALM | 0.53 0.01 | 0.03 0.00 | 52.72 2.00 | 75.56 4.92 | 75.20 4.97 | 65.88 3.06 | 0.40 0.65 |
| Sharp Min–Max | 0.43 0.08 | 0.03 0.02 | 42.78 2.64 | 69.40 7.22 | 69.00 7.31 | 57.32 4.63 | 3.40 2.72 |
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.60 | 0.82 | 81.3 | 80.3 | 81.0 | 80.9 | 84.5 |
| Single AdamW | 0.50 0.01 | 0.00 0.00 | 54.64 0.40 | 66.67 0.60 | 39.00 1.58 | 50.88 0.98 | 0.50 0.71 |
| Dual AdamW | 0.54 0.00 | 0.01 0.01 | 65.20 0.84 | 76.07 0.60 | 62.60 1.67 | 67.47 0.79 | 0.60 0.89 |
| Dual AdamW + ALM | 0.55 0.00 | 0.01 0.00 | 65.40 0.47 | 76.92 0.60 | 65.40 1.14 | 68.83 0.65 | 0.40 0.42 |
| Sharp Min–Max | 0.58 0.00 | 0.02 0.00 | 85.44 0.91 | 75.38 0.72 | 78.80 0.84 | 79.66 0.46 | 0.35 0.34 |
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.55 | 0.48 | 56.8 | 79.5 | 77.0 | 69.5 | 67.0 |
| Single AdamW | 0.43 0.02 | 0.02 0.01 | 42.54 2.04 | 67.86 4.96 | 26.20 4.44 | 38.95 3.23 | 1.56 1.48 |
| Dual AdamW | 0.44 0.16 | 0.01 0.01 | 49.00 4.04 | 62.74 28.51 | 59.40 11.46 | 52.99 3.80 | 0.46 0.62 |
| Dual AdamW + ALM | 0.53 0.01 | 0.03 0.01 | 52.32 2.33 | 78.62 4.22 | 73.20 6.50 | 60.86 2.17 | 1.80 0.92 |
| Sharp Min–Max | 0.45 0.06 | 0.05 0.01 | 46.82 1.10 | 69.58 4.04 | 34.00 12.73 | 38.05 10.21 | 3.46 2.11 |
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.67 | 0.99 | 94.0 | 88.0 | 88.0 | 89.91 | 100 |
| Single AdamW | 0.63 0.03 | 0.02 0.00 | 73.10 1.68 | 62.80 5.12 | 81.30 2.18 | 71.59 1.86 | 6.40 0.34 |
| Dual AdamW | 0.65 0.05 | 0.01 0.01 | 72.40 2.94 | 67.40 4.05 | 79.80 1.66 | 72.85 1.19 | 3.80 0.15 |
| Dual AdamW + ALM | 0.65 0.08 | 0.01 0.04 | 73.50 2.42 | 68.10 2.91 | 78.40 1.91 | 73.09 0.50 | 2.70 0.29 |
| Sharp Min–Max | 0.59 0.15 | 0.03 0.03 | 75.80 1.96 | 72.10 1.91 | 81.20 2.08 | 76.19 0.09 | 5.40 0.18 |
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.68 | 0.94 | 94.0 | 88.0 | 88.0 | 89.91 | 95.0 |
| Single AdamW | 0.61 0.04 | 0.02 0.02 | 69.70 5.42 | 61.40 5.31 | 78.50 1.43 | 69.17 2.80 | 2.25 0.16 |
| Dual AdamW | 0.63 0.16 | 0.02 0.03 | 72.40 4.31 | 69.40 1.92 | 83.10 2.41 | 74.52 2.57 | 0.43 0.05 |
| Dual AdamW + ALM | 0.64 0.04 | 0.00 0.04 | 73.50 8.13 | 72.10 0.84 | 82.70 3.81 | 75.82 1.90 | 0.75 0.75 |
| Sharp Min–Max | 0.62 0.07 | 0.02 0.08 | 71.70 2.46 | 68.40 1.37 | 84.30 1.61 | 74.20 1.71 | 1.25 0.04 |
| Method | Automatic | GPT-based | |||||
| MU | Retain | World Facts | Real Authors | HM | Forget | ||
| Original Model | 0.67 | 0.98 | 93.25 | 88.0 | 88.0 | 89.68 | 95.75 |
| Single AdamW | 0.63 0.06 | 0.00 0.04 | 73.10 1.51 | 64.00 1.09 | 85.40 0.98 | 73.14 1.15 | 1.75 0.02 |
| Dual AdamW | 0.63 0.07 | 0.03 0.02 | 70.70 0.54 | 68.00 2.80 | 87.40 0.54 | 74.46 0.74 | 1.40 0.00 |
| Dual AdamW + ALM | 0.63 0.10 | 0.00 0.02 | 74.50 0.85 | 70.00 0.50 | 90.59 0.81 | 77.42 0.68 | 6.00 0.02 |
| Sharp Min–Max | 0.61 0.15 | 0.01 0.05 | 68.40 0.91 | 67.00 0.91 | 88.10 1.64 | 73.36 1.07 | 4.00 0.04 |
| Method | SAUL | SAUL w/o SAM | Dual-AdamW | Sharp Min–Max |
| Time (s) | 267 | 221 | 164 | 232 |
| Method | SAUL | Dual-AdamW |
| Peak Memory (MB) | 86459.18 | 81834.65 |
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