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Investigating Layer Importance in Large Language Models

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arxiv 2409.14381 v1 pith:VITLZQIE submitted 2024-09-22 cs.CL cs.LG

classification cs.CLcs.LG
keywords layersllmscornerstonelayermodelsperformanceimportanceinvestigating
verification ladder T0 review T1 audit T2 compute T3 formal
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Large language models (LLMs) have gained increasing attention due to their prominent ability to understand and process texts. Nevertheless, LLMs largely remain opaque. The lack of understanding of LLMs has obstructed the deployment in safety-critical scenarios and hindered the development of better models. In this study, we advance the understanding of LLM by investigating the significance of individual layers in LLMs. We propose an efficient sampling method to faithfully evaluate the importance of layers using Shapley values, a widely used explanation framework in feature attribution and data valuation. In addition, we conduct layer ablation experiments to assess the performance degradation resulting from the exclusion of specific layers. Our findings reveal the existence of cornerstone layers, wherein certain early layers can exhibit a dominant contribution over others. Removing one cornerstone layer leads to a drastic collapse of the model performance, often reducing it to random guessing. Conversely, removing non-cornerstone layers results in only marginal performance changes. This study identifies cornerstone layers in LLMs and underscores their critical role for future research.

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Cited by 5 Pith papers

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

  1. A Comprehensive Study of Decoder-Only LLMs for Text-to-Image Generation

    cs.CV 2025-06 conditional novelty 7.0 of 10

    Layer-normalized averaging of all decoder-only LLM hidden states, rather than last-layer embeddings, improves text-to-image compositional alignment and beats T5 on GenAI-Bench.

  2. You Had One Job: Per-Task Quantization Using LLMs' Hidden Representations

    cs.CL 2025-11 reject novelty 6.0 of 10

    TAQ estimates per-layer importance from hidden representations and output sensitivity on task calibration data to allocate mixed precision in a training-free PTQ setting, outperforming task-agnostic baselines on accur...

  3. EvolKV: Evolutionary KV Cache Compression for LLM Inference

    cs.LG 2025-09 conditional novelty 6.0 of 10

    CMA-ES search over per-layer KV cache budgets beats uniform and pyramidal compression heuristics on LongBench, NIAH, RULER, and GSM8K, and edges past the full cache on one code dataset at 1.5% of the budget.

  4. DipSVD: Dual-importance Protected SVD for Efficient LLM Compression

    cs.LG 2025-06 reject novelty 5.0 of 10

    DipSVD combines channel-weighted whitening with layer-wise compression ratios and reports better perplexity and accuracy than existing SVD-based LLM compression methods.

  5. A Survey on Latent Reasoning

    cs.CL 2025-07 conditional novelty 4.0 of 10

    A survey that organizes latent reasoning methods into vertical recurrence, horizontal recurrence, and infinite-depth diffusion, arguing that silent reasoning can beat explicit chain-of-thought.

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