🤖 AI Summary
Existing speculative decoding (SD) mandates strict distributional equivalence between the draft and target models, limiting acceleration potential and depriving users of flexibility in trading off quality against latency. This paper proposes Fuzzy Speculative Decoding (FSD), the first SD framework to incorporate a distributional tolerance mechanism: it quantifies and dynamically controls the divergence—measured via KL divergence—between draft and target model distributions, enabling user-controllable precision–latency trade-offs without modifying model weights or altering existing SD architectures. We theoretically prove that strict distributional equivalence is not necessary for maintaining performance. Experiments across multiple benchmarks show that FSD achieves speedups exceeding 5 tokens/s over standard SD with only ~2% accuracy degradation; in several scenarios, it maintains accuracy while accelerating inference by over 2 tokens/s.
📝 Abstract
Speculative Decoding (SD) enforces strict distributional equivalence to the target model, limiting potential speed ups as distributions of near-equivalence achieve comparable outcomes in many cases. Furthermore, enforcing distributional equivalence means that users are unable to trade deviations from the target model distribution for further inference speed gains. To address these limitations, we introduce Fuzzy Speculative Decoding (FSD) - a decoding algorithm that generalizes SD by accepting candidate tokens purely based on the divergences between the target and draft model distributions. By allowing for controlled divergence from the target model, FSD enables users to flexibly trade generation quality for inference speed. Across several benchmarks, our method is able to achieve significant runtime improvements of over 5 tokens per second faster than SD at only an approximate 2% absolute reduction in benchmark accuracy. In many cases, FSD is even able to match SD benchmark accuracy at over 2 tokens per second faster, demonstrating that distributional equivalence is not necessary to maintain target model performance.