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The Surprising Effectiveness of Deleting Weights in LLM Post-Training

/ Paper arXiv 2611.10866

Curator's notes

Zeroing less than 0.05% of LLM weights via a learned binary maskbinary maskA vector of 0/1 values that selects which weights to keep or delete. matches full fine‑tuning across several post‑training tasks.

Curator's notesWritten by AI from the paperEvery number here appears in the abstractReport a mistake

What's new

Introduces Deletion Tuning, a mask‑only method that achieves full fine‑tuning performance while using a tiny checkpoint and causing minimal forgetting.

Key result

Zeroing fewer than 0.05% of weights matches full fine‑tuning performance across reinforcement learning, supervised fine‑tuning, and on‑policy distillation.

Why it matters

Developers can adapt large models with negligible storage and reduced catastrophic forgetting.

Key numbers

0.05%We find that zeroing fewer than 0.05% of its weights

From the paperCopied from the abstract, not written by AI.

Why this ranked

MeasuredPublic numbers, not AIHow ranking works

63 / 100#2 of 198 papers that day, from GitHub, Hugging Face, Hacker News and Semantic Scholar, looked up the morning it was ranked.

Builder evidence32 / 40

  • Code released
  • ★ 63 GitHub stars
  • +63 stars since the day before
  • 2 models on Hugging Face

Community attention20.4 / 30

Author track record2.5 / 15

  • From agentic learning ai lab

What the paper shows7.9 / 15

  • 1 benchmark result, each found word for word in the abstract
  • Less like recent papers than 78% of that day's candidates

Extracted by AI, checked by codeEach result was found by the model and kept only because its sentence and number appear word for word in the abstract.

  1. prior-task accuracy 5.4 points loss compared to full fine-tuningUnder reinforcement learning, its prior-task accuracy stays near the base level while FFT, LoRA, and random sparse fine-tuning lose up to 5.4 points.

Tie-break. This paper was within 3 points of the next one, so an AI editor compared the leaders and preferred it in 1 of 1 comparisons: “Deletion Tuning offers a genuinely new, lightweight fine‑tuning method with strong quantitative results and released code.”

Abstract

From the paperThe authors' own words.

How little of a pretrained large language model (LLM) has to change for it to acquire new capabilities? We find that zeroing fewer than 0.05% of its weights, with no other modification, matches full fine-tuning (FFT) at scale across three LLM post-training regimes: reinforcement learning with verifiable rewards, supervised fine-tuning, and on-policy distillation. Our method, Deletion Tuning, learns a binary mask over the gate projection of transformer blocks. Two practical advantages follow: the trained mask is hundreds to thousands of times smaller than the corresponding FFT checkpoint, and Deletion Tuning forgets far less, which addresses a central challenge in continual learning. Under reinforcement learning, its prior-task accuracy stays near the base level while FFT, LoRA, and random sparse fine-tuning lose up to 5.4 points. To understand why masking alone suffices, we analyze the geometry of the learned weight changes under reinforcement learning using stable rankstable rankA measure of matrix complexity based on its singular values., spectrum drift, and principal-weight overlapprincipal-weight overlapSimilarity between dominant directions of weight changes in different training regimes.. Compared with LoRA and random sparse fine-tuning, Deletion Tuning is closest to FFT across the three measures.

From the full paper

From the paperCopied from the paper itself by our code.

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What you could build

Written by AIIntermediateRequires understanding of transformer gating and mask optimization, but no massive compute beyond standard fine‑tuning.

  1. Create a tool that generates deletion masks for custom downstream tasks.
  2. Implement a continual‑learning system that swaps masks instead of full model updates.
  3. Build a lightweight model‑serving pipeline that stores only masks for multiple task versions.

Where it fits

The most cited papers it builds on, and the papers that build on it.

/ Builds on 3 most cited

  1. 201733.5k citedProximal Policy Optimization Algorithms ↗
  2. 202225.9k citedTraining language models to follow instructions with human feedback ↗
  3. 202125.7k citedLoRA: Low-Rank Adaptation of Large Language Models ↗

/ Built on by None yet

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Try it

Code, models and demos that use this paper.

Models:
Jacklu0831/deletion-tuning-masks ↗2 models on Hugging Face

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    What proportion of weights does Deletion Tuning zero to match full fine‑tuning performance?

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