arXiv AI

Ghosted Layers: Unconstrained Activation Alignment for Recovering Layer-Pruned LLMs

arXiv:2605. 15491v2 Announce Type: replace-cross Abstract: Layer pruning removes entire Transformer decoder blocks from large language models, but introduces a mismatch between the hidden state received by the next surviving layer and the distribution it was trained to process, leading to significant performance degradation.

arXiv Computer Vision
Aug 27

SHIFT-LLM: Distribution Shift Correction in Depth-Pruned LLMs

SHIFT-LLM is a training‑free post‑pruning correction framework that inserts a Linear Residual Adapter (LRA) at each depth‑pruned site in large language models. Each LRA preserves the original residual identity while adding a lightweight affine correction calibrated via closed‑form least‑squares regression on a small held‑out set, thereby approximating the hidden state that would have been produced by the removed block. Experiments across multiple model families and benchmarks show that SHIFT‑LLM consistently recovers accuracy lost to depth pruning, achieving gains up to +15.7 points on Llama‑3.1‑8B‑Instruct with only a few hundred calibration samples and no gradient computation.

By Ali Bahri, Hang Li, Hongliang Li, Zhitang Chen
arXiv AI
Sep 11

Forward-Free LLM Depth Pruning via Weight Redundancy

The paper introduces Weight-Redundancy Pruning (WRP), a forward‑free depth‑pruning technique for large language models that estimates inter‑layer redundancy using only checkpoint weights. WRP compares attention outputs and MLP down‑projection weights across layers, combining pairwise similarities with relative projection‑scale information to guide layer grouping and block selection. Experiments show that WRP consistently outperforms existing forward‑free magnitude pruning methods and approaches the performance of activation‑based pruning across various pruning settings, model families, and downstream tasks.

By Vincent-Daniel Yun, Woosang Lim
arXiv Machine Learning
Aug 27

When Pruning Meets Interpretability: Preserving Sparse Autoencoder Robustness in LLMs

Sparse autoencoders (SAEs) are commonly used to interpret large language models, but their reliability after pruning is unclear. This study shows that pruning’s effect on an SAE is governed by perturbation energy, a covariance-weighted norm, and that magnitude pruning distorts the representation space by ignoring activation geometry. Activation-aware pruning methods such as Wanda and SparseGPT better preserve SAE behavior, and the authors find that middle layers are especially vulnerable, leading them to propose a layer‑wise sparsity allocation that reduces perplexity for a given sparsity level.

By Suchit Gupte, Xueru Zhang, Mohammad Mahdi Khalili
arXiv Machine Learning
Aug 10

The Sparsity Whisperer

arXiv:2608. 06630v1 Announce Type: new Abstract: Pruning reduces the inference cost of large language models, but existing criteria primarily preserve large activations or reconstruct layer outputs.

By Linghao Kong, Inimai Subramanian, Micah Adler, Dan Alistarh, Dan Gutfreund, Nir Shavit
arXiv Machine Learning
Aug 10

Prune Once: Retraining-Free Task-Agnostic Pruning for Vision-Language Models

arXiv:2608. 06901v1 Announce Type: cross Abstract: Vision-language models (VLMs) have achieved remarkable generalization across diverse multimodal tasks through large-scale pre-training, yet their rapidly increasing computational and memory requirements pose significant challenges for deployment in constrained environments.

By Minseok Kang, Hyunwoo Kim, Chanyoung Kim, Minwoo Kim, Jaekoo Lee, Dahuin Jung