Draft models for speculative decoding were trained against the wrong signal
AspireAI community · arXiv
Speculative decoding accelerates inference by having a small draft model propose tokens that the target verifies in one forward pass. Verification is sequential - everything from the first rejection onward is discarded - yet existing draft training uses token-level imitation of the target with a fixed per-position weighting that reflects neither property. Verification-Aware Training (VAT) simulates verification at every training step and turns the resulting accept and reject patterns into supervision, in two parts: a lightweight jointly-trained verification head that supervises the draft model on whether each position survives sequential verification, and verification-adaptive weighting that keeps full weight up to each sample's first rejection and re-anchors the decay from there. It changes only the training objective, so it layers onto existing methods without touching the draft architecture, the target model, or the inference procedure. Applied to EAGLE-3 and DFlash on Qwen3-4B, Qwen3-8B and LLaMA-3.1-8B, the authors report up to 11.4% higher average acceptance length and up to 8.7% wall-clock speedup, with consistent gains across math, code and chat benchmarks. NeurIPS 2026.
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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.