OpenAttention kept 99% of dense attention accuracy while reading 1% of the KV cache, and its decode kernel ran 10x faster than dense
AspireAI community · arXiv
Sparse attention reads only a small slice of the key-value cache, and the unread tail is where the method matters: discarding it biases the output, and sampling it fails at reads of 5% and below where the tail likely holds heavy hitters the selector missed. The authors' observation is that one proxy token folding the entire tail into a count-aware mean already yields lower output error than a sample at every read behind a practical selector, and they show in closed form that at low reads sampling nearly doubles the weight error of discarding. OpenAttention combines clustering, an ErrorGate that allocates reads by estimated weight error, top-k selection and that count-aware proxy, with training-free query-geometry clustering and selection; on RULER-32K HARD with Llama-3.1-8B it retains 99% of dense accuracy at a 1% read and its custom kernel runs the decode attention stage 10x faster than dense at that read. The paper's headline accuracy numbers are on RULER and related long-context suites rather than on general instruction-following quality.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.