Qwen3.8-27B-DFlash2-Exp

An experimental DFlash2 drafter for Qwen/Qwen3.8-27B.

This checkpoint uses a 7-query sample_from_anchor=true layout that produces seven draft proposals from seven query positions instead of eight, reducing draft-side query compute.

Results

Setting Value
Engine vLLM
Hardware NVIDIA H200, TP1
Concurrency 1
Thinking sampling temperature=1.0, top_p=0.95, top_k=20, min_p=0.0, presence_penalty=0.0, repetition_penalty=1.0
Thinking mode reasoning_effort=xhigh, enable_thinking=true
Non-thinking sampling temperature=0.7, top_p=0.8, top_k=20, min_p=0.0, presence_penalty=1.5, repetition_penalty=1.0
Non-thinking mode enable_thinking=false
Max new tokens 4,096
Context native 262,144
Draft tokens 7 per verification step
Dataset Samples Thinking (xhigh) AL Non-thinking AL
AA-LCR 100 3.8475 4.3578
AIME26 30 2.9922 5.2214
GSM8K 1,319 3.8272 5.5458
HumanEval 164 3.3457 6.5176
LiveCodeBench 1,055 2.7684 4.5785
LongBench-v2 402 3.4772 3.7079
MATH500 500 3.4836 5.7381
MBPP 257 3.2696 5.4883
MMSpec 600 3.1216 3.3236
MT-Bench 80 2.8316 3.5207
SWE-bench Pro 731 2.6905 3.8953

Accepted length is calculated from the raw server counters:

accepted_length = 1 + accepted_tokens / draft_calls

Architecture

Setting Value
Draft layers 5
Auxiliary hidden-state IDs [6, 20, 34, 48, 62]
Hidden size 5,120
FFN intermediate 17,408
Attention 32 Q heads / 8 KV heads
Head dimension 128
Attention window sliding window 2,048
Draft attention non-causal inside the draft block
RoPE theta 1e7
Norm / activation RMSNorm eps 1e-6 / SiLU
Block 7 draft tokens, sample_from_anchor=true
Dynamic convolution kernel 2, group 16
Candidate selector rank 256, top-k 16
Draft vocabulary 248,320
Parameters 1,924,404,480

Training data

A decontaminated, redistributable subset of the training corpus is released as DaoCloud/Qwen3.8-27B-Drafter-SFT.

Example: Run with vLLM

This is a drafter checkpoint, not a standalone language model. Pair it with Qwen3.8-27B or a compatible quantized version:

vllm serve Qwen/Qwen3.8-27B \
  --tensor-parallel-size 1 \
  --enable-auto-tool-choice \
  --tool-call-parser qwen3_coder \
  --reasoning-parser qwen3 \
  --mm-encoder-tp-mode data \
  --speculative-config '{
    "method": "dflash",
    "model": "DaoCloud/Qwen3.8-27B-DFlash2-Exp",
    "num_speculative_tokens": 7
  }'

This checkpoint uses the 7-query sample_from_anchor=true layout and currently requires vLLM PR #54154.

Checkpoint

The BF16 checkpoint contains 81 tensors and 1,924,404,480 parameters. It is released as a 3,848,817,920-byte (3.584 GiB) safetensors file.

File SHA256
model.safetensors 9e1aad9323c3ffecc35b1130e222476f722238233263e7ef9f08389bf1ff2a04

Future work

  • Adaptive verification: explore confidence-head-driven adaptive draft budgets for high-concurrency serving, including varlen GDN support (vLLM #51869).
  • MoE drafter: explore sparsely activated drafter architectures for large-scale serving, increasing model capacity without proportionally increasing active compute.

License

Apache-2.0.

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