POSS: Position Specialist Generates Better Draft for Speculative
  Decoding
Authors: name: Langlin Huang; name: Chengsong Huang; name: Jixuan Leng; name: Di Huang; name: Jiaxin Huang
Published: 2025-06-04 04:30:30

Abstract: Speculative decoding accelerates Large Language Model (LLM) inference by
using a small draft model to predict multiple tokens, and a large target model
to verify these tokens in parallel. Recent studies leverage the hidden state of
the target model to enhance draft model prediction accuracy. However, existing
methods suffer from the degrading quality of draft token predictions at later
positions, due to error accumulation in draft model generated features. In this
paper, we propose Position Specialists (PosS), which consist of multiple
position-specialized draft layers to generate tokens at assigned position(s).
Position specialists greatly improve token acceptance rate at later positions
per drafting round, as each specialist only needs to focus on handling a
certain level of draft model feature deviation. Experiment results on
Llama-3-8B-Instruct and Llama-2-13B-chat across six datasets demonstrate that
PosS effectively improves over baselines on average acceptance length and
speed-up ratio. Our codebase is available at https://github.com/shrango/PosS.