sgl-project/sglang

[Feature] Overlap Spec Support

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#11,762 opened on Oct 17, 2025

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 (24 comments) (25 reactions) (2 assignees)Python (28,442 stars) (6,216 forks)auto 404
enhancementgood first issuehelp wantedhigh priority

Description

Motivation

We have already implemented the initial support for eagle speculative decoding with the overlap scheduler, and here is the roadmap for more feature optimizations and support. The initial skeleton code is this PR https://github.com/sgl-project/sglang/pull/11398

The design illustration is here

[!NOTE] The arg --enable-beta-spec has been deprecated, please use export SGLANG_ENABLE_SPEC_V2=1 to enable this feature.

page size & topk support

  • Support page size > 1 @cicirori @hnyls2002 #11772
  • Support topk > 1 @vincentzed #11839
  • Support topk > 1 + page size > 1 @vincentzed

memory allocation

  • over-allocation optimization @hnyls2002
  • over-allocation with page size > 1 + topk > 1

Attention backend support

sampling

speculative methods

  • new speculative model worker interface (https://github.com/sgl-project/sglang/pull/11643)
  • standalone speculative support @Qiaolin-Yu
  • ngram speculative support @a4zhangfei
  • Top SpecTpWorker for all speculative decoding backends @hnyls2002
  • Make SpecTpWorker compatible with all TpModelWorker features.
  • specialize for high throughput case (num_step=1, topk=1, num_verify_forward_pass_tokens=2) @yukavio

DP attention support

  • Support idle batch @iforgetmyname
    • #12443
  • cover testcases with dp-attention + overlap + spec @iforgetmyname

EP support

  • Check compatibility with DeepEP / EP @fzyzcjy
  • Cover testcases with EP + overlap + spec @fzyzcjy

PD disaggregation

  • Event loop adjust in Prefill / Decode worker @shaharmor98
  • Cover testcases with PD-Disagg + overlap + spec @ShangmingCai

LoRA Support

Aggressive Optimizations

  • Enable a separate `plan_stream

Related resources

No response

Contributor guide

Tech stack
python
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Python
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15
Research direction
Examine the existing overlap spec implementation and understand the speculative decoding architecture in SGLang. Review the linked PRs and design document to get an overview of the components involved.