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Speculative decoding on sparse mixture-of-experts models scales better at small batch sizes than the old models predicted

AspireAI community · arXiv (Ekagra Ranjan, Komal K. Teru, Bharat Venkitesh)
Prior work predicted a concave speedup-to-batch-size relationship for speculative decoding on mixture-of-experts models, with gains peaking at intermediate batch sizes because of expert saturation. This evaluation across 10 sparse MoE models spanning 30B to 1T parameters and 8 to 512 experts finds that recent fine-grained models break that trend and show higher speedup at low batch size. The reason is that verification cost is governed not only by activated-expert bytes but by temporal overlap across draft tokens and GPU execution dynamics, with kernel profiling on H100 attributing the effect mainly to higher bandwidth utilization of MoE kernels relative to attention. The authors model this with a maximum-entropy Iterative Proportional Fitting framework that predicts unique expert counts from routing-overlap statistics with less than 4 percent error, and note the finding is specific to fine-grained sparse models rather than a general law.
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