Adamas: Hadamard Sparse Attention for Efficient Long-Context Inference
Authors: name: Siyuan Yan; name: Guo-Qing Jiang; name: Yuchen Zhang; name: Xiaoxing Ma; name: Ran Zhu; name: Chun Cao; name: Jingwei Xu
Published: 2025-10-21 08:44:47

Abstract: Large language models (LLMs) now support context windows of hundreds of
thousands to millions of tokens, enabling applications such as long-document
summarization, large-scale code synthesis, multi-document question answering
and persistent multi-turn dialogue. However, such extended contexts exacerbate
the quadratic cost of self-attention, leading to severe latency in
autoregressive decoding. Existing sparse attention methods alleviate these
costs but rely on heuristic patterns that struggle to recall critical key-value
(KV) pairs for each query, resulting in accuracy degradation. We introduce
Adamas, a lightweight yet highly accurate sparse attention mechanism designed
for long-context inference. Adamas applies the Hadamard transform,
bucketization and 2-bit compression to produce compact representations, and
leverages Manhattan-distance estimation for efficient top-k selections.
Experiments show that Adamas matches the accuracy of full attention with only a
64-token budget, achieves near-lossless performance at 128, and supports up to
8x higher sparsity than prior state-of-the-art (SOTA) methods while delivering
up to 4.4x self-attention and 1.5x end-to-end speedups on 32K-length sequences.
Remarkably, Adamas attains comparable or even lower perplexity than full
attention, underscoring its effectiveness in maintaining accuracy under
aggressive sparsity.