MixGRPO:
Unlocking Flow-based GRPO Efficiency with Mixed ODE-SDE

Junzhe Li^1,2,3*, Yutao Cui^1*, Tao Huang¹, Yinping Ma³, Chun Fan³, Miles Yang¹, Zhao Zhong¹

¹Hunyuan, Tencent 
²School of Computer Science, Peking University 
³Computer Center, Peking University 

• [2025/7/30] We released the model checkpoint fine-tuned based on FLUX.1 Dev using the MixGRPO algorithm, with HPSv2, ImageReward, and Pick Score as multi-rewards !
• [2025/7/30] We released the paper and code !

• Take comparison with the FlowGRPO and update our technical report.

conda create -n MixGRPO python=3.12
conda activate MixGRPO

sudo yum install -y pdsh pssh mesa-libGL # centos
bash env_setup.sh

The environment dependency is basically the same as DanceGRPO.

Download the FLUX HuggingFace repository to "./data/flux".

mkdir ./data/flux
huggingface-cli login
huggingface-cli download --resume-download  black-forest-labs/FLUX.1-dev --local-dir ./data/flux

Download the code of HPSv2.

git clone https://github.com/tgxs002/HPSv2.git

Download the "HPS_v2.1_compressed.pt" and "open_clip_model.safetensors" to "./hps_ckpt"

mkdir hps_ckpt
huggingface-cli login
huggingface-cli download --resume-download xswu/HPSv2 HPS_v2.1_compressed.pt --local-dir ./hps_ckpt/
huggingface-cli download --resume-download laion/CLIP-ViT-H-14-laion2B-s32B-b79K open_clip_pytorch_model.bin --local-dir ./hps_ckpt/

Run the demo code to automatically download to "~/.cache/huggingface":

python fastvideo/models/reward_model/pick_score.py \
    --device cuda \
    --http_proxy <Your HTTP_PROXY> \ # Default is None
    --https_proxy <Your HTTPS_PROXY>  # Default is None

Down the "ImageReward.pt" and "med_config.json" to "./image_reward_ckpt"

huggingface-cli login
huggingface-cli download --resume-download THUDM/ImageReward med_config.json --local-dir ./image_reward_ckpt/
huggingface-cli download --resume-download THUDM/ImageReward ImageReward.pt --local-dir ./image_reward_ckpt/

Run the demo code to automatically download to "~/.cache/huggingface":

python fastvideo/models/reward_model/clip_score.py \
    --device cuda \
    --http_proxy <Your HTTP_PROXY> \ # Default is None
    --https_proxy <Your HTTPS_PROXY>  # Default is None

Adjust the prompt_path parameter in "./scripts/preprocess/preprocess_flux_rl_embeddings.sh" to obtain the embeddings of the prompt dataset.

bash scripts/preprocess/preprocess_flux_rl_embeddings.sh

The training dataset is the training prompts in HPDv2, as shown in "./data/prompts.txt"

We use the "pdsh" command for multi-node training with "torchrun". The default resource configuration consists of 4 nodes, each with 8 GPUs, totaling 32 GPUs.

First, set your multi-node IPs in the data/hosts/hostfile.

Then, run the following script to set the environment variable INDEX_CUSTOM on each node to 0, 1, 2, and 3, respectively.

bash scripts/preprocess/set_env_multinode.sh

Next, set the wandb_key to your Weights & Biases (WandB) key in "./scripts/finetune/finetune_flux_grpo_FastGRPO.sh".

Finally, run the following training script:

bash scripts/finetune/finetune_flux_grpo_FastGRPO.sh

The test dataset is also the test prompts in HPDv2, as shown in "./data/prompts_test.txt"

First, you need to download the MixGRPO model weight "diffusion_pytorch_model.safetensors" to the "./mix_grpo_ckpt" directory.

mkdir mix_grpo_ckpt
huggingface-cli login
huggingface-cli download --resume-download tulvgengenr/MixGRPO diffusion_pytorch_model.safetensors --local-dir ./mix_grpo_ckpt/

Then, adjust the Input parameters in "scripts/inference/inference_flux.sh" (currently set to default) and then execute the single-node script.

bash scripts/inference/inference_flux.sh

Set prompt_file to the path of the JSON file generated during inference in "scripts/evaluate/eval_reward.sh". Then run the following single-node script.

bash scripts/evaluate/eval_reward.sh

We are deeply grateful for the following GitHub repositories, as their valuable code and efforts have been incredibly helpful:

• DanceGRPO
• Flow-GRPO
• FastVideo
• HPSv2

MixGRPO is licensed under the License Terms of MixGRPO. See ./License.txt for more details.

If you find MixGRPO useful for your research and applications, please cite using this BibTeX:

@misc{li2025mixgrpounlockingflowbasedgrpo,
      title={MixGRPO: Unlocking Flow-based GRPO Efficiency with Mixed ODE-SDE}, 
      author={Junzhe Li and Yutao Cui and Tao Huang and Yinping Ma and Chun Fan and Miles Yang and Zhao Zhong},
      year={2025},
      eprint={2507.21802},
      archivePrefix={arXiv},
      primaryClass={cs.AI},
      url={https://arxiv.org/abs/2507.21802}, 
}