On Length Normalization in the Code

Simple Preference Optimization (SimPO)

This repository contains the code and released models for our paper SimPO: Simple Preference Optimization with a Reference-Free Reward. We propose a simpler and more effective preference optimization algorithm than DPO (Direct Preference Optimization) without using a reference model. SimPO outperforms DPO and its latest variants across AlpacaEval 2, MT-Bench, and Arena-Hard benchmarks under various settings.

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SimPO: Simple Preference Optimization with a Reference-Free Reward

Released Models

Below is the full list of models that we evaluate in our preprint.

models		AE2 LC	AE2 WR	AH
Mistral Base 7B SFT	alignment-handbook/zephyr-7b-sft-full	8.4	6.2	1.3
Mistral Base 7B DPO (Zephyr)	princeton-nlp/Mistral-7B-Base-SFT-DPO	15.1	12.5	10.4
Mistral Base 7B IPO	princeton-nlp/Mistral-7B-Base-SFT-IPO	11.8	9.4	7.5
Mistral Base 7B KTO	princeton-nlp/Mistral-7B-Base-SFT-KTO	13.1	9.1	5.6
Mistral Base 7B ORPO	kaist-ai/mistral-orpo-beta	14.7	12.2	7.0
Mistral Base 7B R-DPO	princeton-nlp/Mistral-7B-Base-SFT-RDPO	17.4	12.8	9.9
Mistral Base 7B SimPO	princeton-nlp/Mistral-7B-Base-SFT-SimPO	21.4	20.8	16.6
Mistral Instruct 7B SFT	mistralai/Mistral-7B-Instruct-v0.2	17.1	14.7	12.6
Mistral Instruct 7B DPO	princeton-nlp/Mistral-7B-Instruct-DPO	26.8	24.9	16.3
Mistral Instruct 7B IPO	princeton-nlp/Mistral-7B-Instruct-IPO	20.3	20.3	16.2
Mistral Instruct 7B KTO	princeton-nlp/Mistral-7B-Instruct-KTO	24.5	23.6	17.9
Mistral Instruct 7B ORPO	princeton-nlp/Mistral-7B-Instruct-ORPO	24.5	24.9	20.8
Mistral Instruct 7B R-DPO	princeton-nlp/Mistral-7B-Instruct-RDPO	27.3	24.5	16.1
Mistral Instruct 7B SimPO	princeton-nlp/Mistral-7B-Instruct-SimPO	32.1	34.8	21.0
Llama3 Base 8B SFT	princeton-nlp/Llama-3-Base-8B-SFT	6.2	4.6	3.3
Llama3 Base 8B DPO	princeton-nlp/Llama-3-Base-8B-SFT-DPO	18.2	15.5	15.9
Llama3 Base 8B IPO	princeton-nlp/Llama-3-Base-8B-SFT-IPO	14.4	14.2	17.8
Llama3 Base 8B KTO	princeton-nlp/Llama-3-Base-8B-SFT-KTO	14.2	12.4	12.5
Llama3 Base 8B ORPO	princeton-nlp/Llama-3-Base-8B-SFT-ORPO	12.2	10.6	10.8
Llama3 Base 8B R-DPO	princeton-nlp/Llama-3-Base-8B-SFT-RDPO	17.6	14.4	17.2
Llama3 Base 8B SimPO	princeton-nlp/Llama-3-Base-8B-SFT-SimPO	22.0	20.3	23.4
Llama3 Instruct 8B SFT	meta-llama/Meta-Llama-3-Instruct-8B	26.0	25.3	22.3
Llama3 Instruct 8B DPO	princeton-nlp/Llama-3-Instruct-8B-DPO	40.3	37.9	32.6
Llama3 Instruct 8B IPO	princeton-nlp/Llama-3-Instruct-8B-IPO	35.6	35.6	30.5
Llama3 Instruct 8B KTO	princeton-nlp/Llama-3-Instruct-8B-KTO	33.1	31.8	26.4
Llama3 Instruct 8B ORPO	princeton-nlp/Llama-3-Instruct-8B-ORPO	28.5	27.4	25.8
Llama3 Instruct 8B R-DPO	princeton-nlp/Llama-3-Instruct-8B-RDPO	41.1	37.8	33.1
Llama3 Instruct 8B SimPO	princeton-nlp/Llama-3-Instruct-8B-SimPO	44.7	40.5	33.8

Please refer to the generate.py script for detailed instructions on loading the model with the appropriate chat template.

Install Requirements

Our codebase is built upon the alignment-handbook repo. The following steps will guide you through the installation process.

First, create a Python virtual environment using e.g. Conda:

conda create -n handbook python=3.10 && conda activate handbook

Next, install PyTorch v2.2.2. Since this is hardware-dependent, we direct you to the PyTorch Installation Page.

You can then install the remaining package dependencies of alignment-handbook as follows:

git clone https://github.com/huggingface/alignment-handbook.git
cd ./alignment-handbook/
python -m pip install .

You will also need Flash Attention 2 installed, which can be done by running:

python -m pip install flash-attn --no-build-isolation

Training Scripts

We provide four training config files for the four training setups reported in our paper. The training config is set for 8xH100 GPUs. You may need to adjust num_processes and per_device_train_batch_size based on your computation environment.

Mistral-Base:

ACCELERATE_LOG_LEVEL=info accelerate launch --config_file accelerate_configs/deepspeed_zero3.yaml scripts/run_simpo.py training_configs/mistral-7b-base-simpo.yaml

Mistral-Instruct:

ACCELERATE_LOG_LEVEL=info accelerate launch --config_file accelerate_configs/deepspeed_zero3.yaml scripts/run_simpo.py training_configs/mistral-7b-instruct-simpo.yaml

Llama3-Base:

ACCELERATE_LOG_LEVEL=info accelerate launch --config_file accelerate_configs/deepspeed_zero3.yaml scripts/run_simpo.py training_configs/llama-3-8b-base-simpo.yaml

Llama3-Instruct:

ACCELERATE_LOG_LEVEL=info accelerate launch --config_file accelerate_configs/deepspeed_zero3.yaml scripts/run_simpo.py training_configs/llama-3-8b-instruct-simpo.yaml

Evaluation

We follow the official implementation for evaluation on AlpacaEval 2, Arena-Hard, and MT-Bench, as follows (more details can be found under the eval directory):

AlpacaEval 2: Please refer to the AlpacaEval repo for evaluation.
Arena-Hard: Please refer to to the Arena-Hard-Auto repo for evaluation.
MT-Bench: Please refer to the FastChat repo for evaluation.

Bugs or Questions?

If you have any questions related to the code or the paper, feel free to email Yu ([email protected]). If you encounter any problems when using the code, or want to report a bug, feel free to open an issue! Please try to specify the problem with details so we can help you better and quicker!

Citation

Please cite our paper if you find the repo helpful in your work:

@article{meng2024simpo,
  title={{SimPO}: Simple Preference Optimization with a Reference-Free Reward},
  author={Meng, Yu and Xia, Mengzhou and Chen, Danqi},
  year={2024}
}