LISA: Linear-Indexed Sparse Attention for Efficient Long-Context Reasoning
To address the quadratic complexity of self-attention in long chain-of-thought reasoning models, this paper proposes LISA, a plug-and-play attention module that reduces inference complexity from O(n²) to O(nM) via parallel linear attention and a lightning indexer, achieving 50% speedup and 5.6% average performance gain on reasoning benchmarks.
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[Submitted on 29 May 2026]
Title:LISA: Linear-Indexed Sparse Attention for Efficient Long-Context Reasoning
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Abstract:Recent advances in long chain-of-thought reasoning models such as DeepSeek-R1 have led to increasingly longer inference context lengths under the test-time scaling paradigm. However, the O(n^2) computational complexity of standard self-attention causes inference costs to grow sharply with long sequences, limiting the deployment of long-CoT reasoning in production settings. To address this, we propose LISA (Linear-Indexed Sparse Attention), a plug-and-play attention replacement module that requires no pretraining from scratch. LISA integrates two lightweight components in parallel within the original model: (1) a Linear Attention module that provides long-range memory with O(n) time complexity; (2) a Lightning Indexer that selects the top-M important tokens from the full context to feed into a Sparse Self-Attention. The two branches are fused via a gating mechanism, reducing inference complexity from O(n^2) to O(nM) (M
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