arXiv AI

Only Accepted Tokens Count: An Energy Accounting of Speculative Decoding Under Latency Targets

The paper investigates how speculative decoding—where a draft model proposes multiple future tokens that are then verified by the target model—affects energy consumption in large language model serving under latency constraints. It finds that energy savings depend heavily on the acceptance rate of drafted tokens, which varies by model architecture, drafting scheme, and the type of text (e.g., conversation vs. code, English vs. Romansh). The study shows that while speculation can reduce energy per token at small batch sizes, at larger batches the verification cost dominates, potentially turning speculation into an energy loss, especially when acceptance rates are low.

arXiv Machine Learning
Oct 3

CAST: Cost-Aware Speculative Trees from One-Pass Block Drafters

CAST (Cost‑Aware Speculative Trees) is a method that improves speculative decoding for large language models by packing multiple drafted token candidates into a tree and verifying the entire tree in a single target‑model pass, rather than only the top‑scoring chain. The tree width is adaptively chosen based on a latency measurement, ensuring that each added candidate’s expected gain outweighs its verification cost. Experiments across five domains, three GPU generations, and two model families show that CAST can be up to 43 % faster than the standard chain, while preserving the target model’s output distribution under both greedy and sampled decoding.

By Jungseob Lee, Sugyeong Eo
arXiv Machine Learning
Oct 16

HyCo: Hybrid Drafting for Cost-Efficient Mobile-Cloud Speculative Decoding

HyCo is a hybrid drafting method that assigns depth to a server model’s multi‑token prediction head for execution on a mobile NPU, while alternative branches are handled by a small language model in a single pass. By returning only the hidden state, input embedding, and key‑value entries, HyCo reduces server GPU time per token by 38.6% on Spec‑Bench and 29.2% on 32K‑token summarization, and achieves faster delivery and higher savings than an SLM‑only drafter. The approach also incorporates quantization, a restricted vocabulary, a 1K‑token window, and an ε‑threshold rule to relax exact sampling distribution preservation.

By Hanbin Bae, Heejin Choi, Joohyung Lee, Byoung Jin Choi, Sangjun Park, Hoon-Young Cho
arXiv Machine Learning
6d ago

One Call Ahead: Packed Self-Speculative Decoding with Diffusion Drafting

The paper introduces Packed-SS, a self‑speculative decoding schedule that combines drafting and verification into a single model call, reducing input size to linear in speculative width. By running the diffusion drafter one step ahead, the method keeps an unresolved suffix for the next iteration, avoiding the sequential wait of standard two‑call decoding. Experiments on Nemotron 3B/8B and SetDLM 1.7B demonstrate higher throughput and lower mean wall time under greedy decoding.

By Yuxiao Chen, Changxiao Cai
arXiv AI
Oct 5

What Does a Token Cost? A Mixture-of-Agents Measurement of Sufficient Per-Token Compute

The paper introduces a Mixture-of-Agents (MoA) approach to quantify the per-token compute required by large language models. By having a panel of fifteen models of varying sizes attempt to reproduce each token, the authors define the smallest successful agent’s inference cost as the token’s sufficient compute, providing an upper bound on necessary computation. Experiments on benchmarks show that a 0.5B model can reproduce most tokens, and that the MoA-derived compute map can reduce latency in model routing and drafting tasks while improving or maintaining accuracy.

By Zhixu Du, Weijia Han, Hai Helen Li, Yiran Chen