Beyond Parallel Blindness: Information Floors and Model Gaps in Block Drafting

2026-08-27

AI Summary

研究通过引入信息底限和模型差距，区分并分析了块起草中信息缺失和建模不完善的问题，揭示了局部条件的重要性和当前模型的改进空间。

Abstract

Block drafters propose several tokens in one forward pass, before earlier target tokens are realised. Their rejection mixes two losses: missing within-block path information and imperfect modelling of observable information. Accepted length cannot distinguish them. We separate the two with an information floor, the minimum expected rejection at a specified conditioning order; rejection above this floor is the model gap. Estimating both from target rollouts across four domains, four open-weight targets, and a frontier API target yields three findings. First, the all-parallel floor reaches $0.286$ at the final slot on Qwen3-4B, limiting even the best proposal to $71\%$ per-slot acceptance. Second, one realised token removes $86$--$100\%$ of this floor, a locality also recovered by an independent mutual-information analysis. Third, current drafters remain far above their floors: the final-slot model gap accounts for $43$--$64\%$ of DFlash rejection and $85$--$92\%$ of DSpark's oracle-conditioned rejection. These findings separate the value of short-range conditioning from proposal quality.

Problem

• block drafting
• information floor
• model gap

Innovation

• information floor
• model gap
• block drafting