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The Sparse Frontier: Sparse Attention Trade-offs in Transformer LLMs

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arxiv 2504.17768 v3 pith:Q2KJM2DX submitted 2025-04-24 cs.CL cs.LG

classification cs.CLcs.LG
keywords sparseattentionmethodssparsityanalysiscostduringestimation
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

Sparse attention offers a promising strategy to extend long-context capabilities in Transformer LLMs, yet its efficiency-accuracy trade-offs remain unclear due to the lack of comprehensive evaluation. We address this gap with the largest-scale empirical analysis to date of training-free sparse attention, evaluating six methods across multiple model families and sizes, sequences up to 128K tokens, and sparsity levels up to 0.95 (i.e., $1/20$ attention budget) on nine diverse tasks. We first organise the rapidly evolving landscape of sparse attention methods into a taxonomy along four design axes. Our analysis then yields actionable insights: 1) sparse attention is effective: larger sparse models outperform smaller dense ones at equivalent cost, improving the Pareto frontier; 2) for the training-free methods we study, fine-grained per-query importance estimation during prefilling remains impractical-due to both the cost of estimation and the lack of sparse kernels that translate fine-grained sparsity into wall-clock gains-forcing a task-dependent choice between global-to-token and block-to-block selection. Instead, during decoding, token-to-page selection becomes feasible, enabling better generalisation and higher sparsity tolerance; 3) longer sequences tolerate higher sparsity, suggesting that fixed-budget methods in production are suboptimal. Together, these findings provide practical guidance for deploying sparse attention and methodological recommendations for future evaluations. Our code is available at https://github.com/PiotrNawrot/sparse-frontier.

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Cited by 8 Pith papers

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

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    Page-local rank-8 spectral key summaries let sparse decode selection track the exact mass oracle and match FullKV quality at ~2% attended tokens with 2× latency cut at 1M context.

  2. Learning What Matters: Supervising Global Context Pruning with Causal Evidence Sets

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    Attention is an unreliable supervision target for context pruning; causal evidence sets recovered by masking produce routers that match or beat attention-distilled routers, especially on multi-hop and conflicting-fact tasks.

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