arXiv Machine Learning

Ceiling-Clipped Acceptance Histograms Indicate Stranded Speed-up in Block-Diffusion Speculative Decoding

arXiv Machine Learning
4d ago

Long-Context Drafting Does Not Require Long-Context Drafters

The paper shows that long‑context drafting can be performed with short‑context drafters that are frozen and run beyond their training length, using two inference‑time mechanisms to keep their cost bounded. By bounding the attention cache and re‑basing rotary position indices, the authors demonstrate that the speedup achieved with a short‑context drafter persists up to two million tokens across multiple target‑drafter pairs and corpora. They prove that when a common index shift leaves the drafter’s computation unchanged, the acceptance gap can be tightly bounded, ensuring consistent performance.

By Aref Jafari, Vansh Bhatia, Matt Qin, Subhajit Dutta Chowdhury, Ben Lee, Vikram Appia, Ali Ghodsi, Mehdi Rezagholizadeh
arXiv AI
Aug 5

Approximate Speculative Decoding

arXiv:2608. 03447v1 Announce Type: cross Abstract: Speculative decoding accelerates autoregressive generation by verifying a draft block with a target model in parallel.

By Yuannuo Feng, Zegang Peng, Yuxin Xie, Yubing Ye, Yizhe Chen, Wenshuai Yao, Wenyong Zhou, Wang Kang
arXiv Computation and Language
1d ago

Acceptance Is Not Speed: Length Inflation in Training-Free Lossy Speculative Decoding

The paper investigates speculative decoding, a technique that speeds up language model inference by generating draft tokens and verifying them. It shows that when verification is relaxed (lossy), the resulting completions become longer—especially due to extended reasoning traces—despite accepting more tokens per round. The study evaluates various relaxed verification rules across multiple model pairs, finding that higher acceptance rates often lead to longer outputs, lower target-model probability tokens, and reduced accuracy, indicating that token acceptance alone is an unreliable metric for decoding speed.

By Chiatzen Wang, Bill Xu, Haochen Gu, Hongyang Zhang
arXiv AI
Oct 9

Where Draft Trees Lose Target Mass: Exit-Guided Speculative Decoding

The paper introduces Tree Exit Verification (TEV), an exact, level‑parallel speculative decoding method that uses a single exit‑node decision and a bonus‑token decision to verify draft continuations. By deriving a canonical exit law, the authors show that TEV achieves the same acceptance as optimal verifiers while reducing verifier‑stage latency by 15%. They also propose Exit‑Guided Draft‑Tree Training (ExitTrain), which improves draft trees and increases average output‑block length by 13%, leading to a 14% end‑to‑end speedup over DDTree across dialogue, code, and mathematical reasoning tasks.

By Shijing Hu, Xuancheng Ren, Zhihui Lu, Pan Zhou
arXiv AI
Sep 2

Vision Is Not Overhead: One-Pass Block Drafting for Lossless Speculative Decoding in Vision-Language Models

The paper introduces GLANCE, a one‑pass block drafting method that enables lossless speculative decoding for vision‑language models. By using a block‑diffusion head that reads the fused vision‑language state, GLANCE eliminates the need for the drafter to process the image at every step, allowing it to fill an entire block in a single forward pass. Experiments show that GLANCE can decode up to 2.93× faster than autoregressive decoding while maintaining exact greedy decoding results across multiple tasks.

By Jungseob Lee, Seongtae Hong, Dongyub Jude Lee, Chanjun Park, Jaehyung Seo, Sugyeong Eo, Heuiseok Lim