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.

🔗 Quick Links

• SimPO: Simple Preference Optimization with a Reference-Free Reward
  • Tips for Running SimPO
  • Released Models
  • Install Requirements
  • Training scripts
  • Evaluation
  • Bugs or Questions?
  • Citation

Tips for Running SimPO

Given the various inquiries about SimPO, we provide a list of tips to help you reproduce our paper results and achieve better outcomes for running SimPO on your own tasks.

Hyperparameter tuning

Hyperparameter tuning is crucial for SimPO. The three main hyperparameters to focus on are learning_rate, beta, and gamma.

• learning_rate: learning_rate: The learning rate is the most critical hyperparameter for preference optimization. A large learning rate (e.g., 1e-5) can significantly degrade performance, causing the model to produce incoherent sentences or completely repetitive responses. We recommend grid searching over 3e-7, 5e-7, and 1e-6, if resources allow.
• `beta: Beta controls the reward scaling between winning and losing responses. In our preprint, we used a small beta (e.g., 2.0 or 2.5), but researchers from Meta suggest that a larger beta (e.g., 10) could yield better results.
• `gamma: Gamma controls the target reward margin. We suggest tuning gamma in tandem with beta, where gamma = c * beta. We recommend grid searching over 0.25, 0.3, and 0.4. A well-tuned gamma can provide a modest improvement, but it is not as critical as other hyperparameters.

We used the following hyperparameters for training the released models.

Setting	β	γ	Learning rate
Mistral-Base	2.0	1.6	3e-7
Mistral-Instruct	2.5	0.3	5e-7
Llama3-Base	2.0	1.0	6e-7
Llama3-Instruct	2.5	1.4	1e-6

Training and evaluation consistency in BOS

Our released Llama3 models use the initial version of the Llama3 tokenizer (prior to this PR). We have found that the updated Llama3 tokenizer with vLLM occasionally introduces two BOS tokens, which can affect evaluation results. Therefore, please ensure that only one BOS token is included in the prompt after applying the Llama3 chat template during any evaluation.

Notably, if you are training Llama3 and evaluating the trained models on AlpacaEval 2 and Arena-Hard using the templates provided in this repo, please make sure to use the pre-update Llama3 tokenizer (i.e., the one before the PR).

Adding an extra sft loss

We have observed that, in some cases, adding an additional SFT loss can help improve results. These findings have been initially validated in the CPO_SIMPO repository. We are currently working on integrating this improvement into our main repository.

Released Models

Below is the complete list of models evaluated 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 (yumeng5@virginia.edu). 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}
}