SparseGDN makes gated linear attention skip most of its own recurrent updates
AspireAI community · arXiv
Gated Delta Networks give linear-time sequence modelling, but long-context prefill stays costly because of dense intra-chunk computation, recurrent-state updates and intermediate state storage. SparseGDN is a hardware-aware framework that combines structured intra-chunk approximation with input-dependent recurrent-event selection while still producing an output for every token: a block-adjacent solver reduces local Delta-solve computation, and a dynamic selector allocates recurrent-update budgets across head pairs, with the GPU implementation materialising updates only for selected events and reconstructing token outputs from compact state snapshots and group-local interactions. Evaluated on Qwen3.5-4B and Qwen3.5-9B across RULER tasks and context lengths from 4K to 128K, the authors report that retaining approximately 29% of recurrent events on average, SparseGDN achieves 1.50-1.94x GDN-core prefill speedups over native FLA kernels, with the online selection overhead included. The limitation is that the speedups are measured against the FLA kernels rather than a general serving stack, and the paper is a preprint with no peer review noted.
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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.