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Screening tokens once and reusing inactive dictionary atoms kept KV cache compression bounded in memory and in decoding cost during long reasoning traces

AspireAI community · arXiv
Dictionary-based sparse KV compression represents each token's key-value state as a sparse combination of learned basis elements, but existing methods either pay iterative sparse-coding overhead at decode time or let a static dictionary drift out of match with the evolving KV distribution, and append-only dictionary updates grow without bound. FAD-KV addresses both with a screening-based sparse coding scheme, where a one-shot top-n selection picks a small candidate pool before lightweight coefficient refinement, and a fixed-size dictionary adaptation mechanism that reuses inactive atoms instead of expanding the dictionary. The authors report a strong quality-efficiency trade-off on reasoning and long-context benchmarks with no unbounded dictionary growth. The evaluation does not report a single headline speedup number, so the practical gain is expressed as a trade-off rather than a fixed multiplier.
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One distance function matched sparse-autoencoder features across layers and compressed feature circuits into supernodes
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.
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