Kimi-K3-DFlash

Kimi-K3-DFlash

Paper | Github | Blog

This repository contains a DFlash draft model for moonshotai/Kimi-K3 trained only on a generic data mix (no tool calls, agentic traces, etc). It is not a standalone language model. It is intended to be paired with the target model in a speculative decoding server.

DFlash uses a lightweight block diffusion draft model to propose multiple tokens in parallel. The target model verifies those proposals, improving serving throughput while preserving the target model's output distribution.

Quick Start

This model should be used with an inference server that supports DFlash speculative decoding. An example SGLang deployment is:

export SGLANG_ENABLE_OVERLAP_PLAN_STREAM=1

python -m sglang.launch_server \
  --model-path moonshotai/Kimi-K3 \
  --trust-remote-code \
  --speculative-algorithm DFLASH \
  --speculative-draft-model-path modal-labs/Kimi-K3-DFlash \
  --speculative-dflash-block-size 16 \
  --speculative-draft-attention-backend trtllm_mha \
  --attention-backend trtllm_mla \
  --linear-attn-prefill-backend ptx_kda \
  --linear-attn-decode-backend triton \
  --linear-attn-verify-backend triton \
  --enable-gdn-replayssm-spec \
  --linear-replayssm-cache-len 32 \
  --moe-runner-backend flashinfer_mxfp4 \
  --cuda-graph-backend-prefill breakable \
  --cuda-graph-max-bs-prefill 16384 \
  --tp-size 8 \
  --mem-fraction-static 0.88 \
  --host 0.0.0.0 \
  --port 30000

Block size 8 is the recommended default. Block size 16 gives longer accept lengths.

Benchmark Results

On certain workloads we have measured peak per-request decode throughput approaching 900 output tok/s at concurrency 1 with an experimental block size 16 nv_cutedsl linear attention verify backend (877 tok/s on GSM8K and 862 tok/s on MATH500).

Setup

• Runtime: SGLang on 8x NVIDIA B300 GPUs, tensor parallel size 8, bfloat16
• Backends: trtllm_mla target attention, trtllm_mha DFlash draft attention, ptx_kda linear attention prefill, triton linear attention decode and verify, flashinfer_mxfp4 MoE runner
• Workloads: GSM8K, MATH500, HumanEval, MBPP, MT-Bench, LongBench-v2 (samples up to 128k tokens), and a long-context HumanEval variant (cold 64k-token prefix) with the Kimi chat template
• Decoding: greedy, thinking enabled, max output length 4096 tokens
• Accept length: completion_tokens / spec_verify_ct per generation turn, averaged across generation turns

Accept Length

Mean accept length at concurrency 1.

Acknowledgements

Special thanks to our close collaborators Jian Chen and Zhijian Liu from Z-Lab — we are deeply grateful for the thoughtful discussions, careful ablations, and genuine spirit of collaboration that made this release possible. This model is also mirrored on their Hugging Face at:

• z-lab/Kimi-K3-DFlash

Citation

If you find DFlash useful, please cite the original paper:

@article{chen2026dflash,
  title   = {{DFlash: Block Diffusion for Flash Speculative Decoding}},
  author  = {Chen, Jian and Liang, Yesheng and Liu, Zhijian},
  journal = {arXiv preprint arXiv:2602.06036},
  year    = {2026}
}