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FlatCake threw out the tiered KV cache: on a production Claude Code trace it held a 94 percent hit rate against Mooncake's 64 and cut peak-load mean TTFT by 1.6 times

AspireAI community · arXiv (FlatCake KV cache storage architecture)
Most LLM serving stacks treat host DRAM and NVMe SSD as a two-tier cache, with DRAM as an intermediate layer. FlatCake argues production agentic traffic breaks both premises, because sessions either reuse blocks too rarely or exceed DRAM entirely, putting SSD on the critical read path, so it exposes DRAM and SSD as peer media in a unified 64-bit address space and writes each immutable, session-scoped KV block straight to its target medium in contiguous layer-major order. On a production Claude Code trace with DeepSeek-V4-Flash it sustains a 94 percent cache hit rate as load rises against 64 percent for Mooncake, removes Mooncake's 6.5 to 6.7 times SSD read amplification, and cuts peak-load mean TTFT by 1.6 times while raising total token throughput by 1.6 times; on 8K to 128K contexts with Llama-3.1-70B it cuts mean TTFT by up to 2.4 times over Mooncake. The honest caveat is that the headline numbers come from the authors' own cluster and their DeepSeek-V4-Flash trace, so the comparison is against Mooncake's published behaviour rather than a neutral third-party serving bake-off.
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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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