Welcome Mixtral - a SOTA Mixture of Experts on Hugging Face

This article is also available in Chinese 简体中文.

Mixtral 8x7b is an exciting large language model released by Mistral today, which sets a new state-of-the-art for open-access models and outperforms GPT-3.5 across many benchmarks. We’re excited to support the launch with a comprehensive integration of Mixtral in the Hugging Face ecosystem 🔥!

Among the features and integrations being released today, we have:

• Models on the Hub, with their model cards and licenses (Apache 2.0)
• 🤗 Transformers integration
• Integration with Inference Endpoints
• Integration with Text Generation Inference for fast and efficient production-ready inference
• An example of fine-tuning Mixtral on a single GPU with 🤗 TRL.

Table of Contents

• What is Mixtral 8x7b
  • About the name
  • Prompt format
  • What we don't know
• Demo
• Inference
  • Using 🤗 Transformers
  • Using Text Generation Inference
• Fine-tuning with 🤗 TRL
• Quantizing Mixtral
  • Load Mixtral with 4-bit quantization
  • Load Mixtral with GPTQ
• Disclaimers and ongoing work
• Additional Resources
• Conclusion

What is Mixtral 8x7b?

Mixtral has a similar architecture to Mistral 7B, but comes with a twist: it’s actually 8 “expert” models in one, thanks to a technique called Mixture of Experts (MoE). For transformers models, the way this works is by replacing some Feed-Forward layers with a sparse MoE layer. A MoE layer contains a router network to select which experts process which tokens most efficiently. In the case of Mixtral, two experts are selected for each timestep, which allows the model to decode at the speed of a 12B parameter-dense model, despite containing 4x the number of effective parameters!

For more details on MoEs, see our accompanying blog post: hf.co/blog/moe

Mixtral release TL;DR;

• Release of base and Instruct versions
• Supports a context length of 32k tokens.
• Outperforms Llama 2 70B and matches or beats GPT3.5 on most benchmarks
• Speaks English, French, German, Spanish, and Italian.
• Good at coding, with 40.2% on HumanEval
• Commercially permissive with an Apache 2.0 license

So how good are the Mixtral models? Here’s an overview of the base model and its performance compared to other open models on the LLM Leaderboard (higher scores are better):

For instruct and chat models, evaluating on benchmarks like MT-Bench or AlpacaEval is better. Below, we show how Mixtral Instruct performs up against the top closed and open access models (higher scores are better):

Impressively, Mixtral Instruct outperforms all other open-access models on MT-Bench and is the first one to achieve comparable performance with GPT-3.5!

About the name

The Mixtral MoE is called Mixtral-8x7B, but it doesn't have 56B parameters. Shortly after the release, we found that some people were misled into thinking that the model behaves similarly to an ensemble of 8 models with 7B parameters each, but that's not how MoE models work. Only some layers of the model (the feed-forward blocks) are replicated; the rest of the parameters are the same as in a 7B model. The total number of parameters is not 56B, but about 45B. A better name could have been Mixtral-45-8e to better convey the architecture. For more details about how MoE works, please refer to our "Mixture of Experts Explained" post.

Prompt format

The base model has no prompt format. Like other base models, it can be used to continue an input sequence with a plausible continuation or for zero-shot/few-shot inference. It’s also a great foundation for fine-tuning your own use case. The Instruct model has a very simple conversation structure.

<s> [INST] User Instruction 1 [/INST] Model answer 1</s> [INST] User instruction 2[/INST]

This format has to be exactly reproduced for effective use. We’ll show later how easy it is to reproduce the instruct prompt with the chat template available in transformers.

What we don't know

Like the previous Mistral 7B release, there are several open questions about this new series of models. In particular, we have no information about the size of the dataset used for pretraining, its composition, or how it was preprocessed.

Similarly, for the Mixtral instruct model, no details have been shared about the fine-tuning datasets or the hyperparameters associated with SFT and DPO.

Demo

You can chat with the Mixtral Instruct model on Hugging Face Chat! Check it out here: https://huggingface.co/chat/?model=mistralai/Mixtral-8x7B-Instruct-v0.1.

Inference

We provide two main ways to run inference with Mixtral models:

• Via the pipeline() function of 🤗 Transformers.
• With Text Generation Inference, which supports advanced features like continuous batching, tensor parallelism, and more, for blazing fast results.

For each method, it is possible to run the model in half-precision (float16) or with quantized weights. Since the Mixtral model is roughly equivalent in size to a 45B parameter dense model, we can estimate the minimum amount of VRAM needed as follows:

Using 🤗 Transformers

With transformers release 4.36, you can use Mixtral and leverage all the tools within the Hugging Face ecosystem, such as:

• training and inference scripts and examples
• safe file format (safetensors)
• integrations with tools such as bitsandbytes (4-bit quantization), PEFT (parameter efficient fine-tuning), and Flash Attention 2
• utilities and helpers to run generation with the model
• mechanisms to export the models to deploy

Make sure to use a recent version of transformers:

pip install --upgrade transformers

In the following code snippet, we show how to run inference with 🤗 Transformers and 4-bit quantization. Due to the large size of the model, you’ll need a card with at least 30 GB of RAM to run it. This includes cards such as A100 (80 or 40GB versions), or A6000 (48 GB).

from transformers import pipeline
import torch

model = "mistralai/Mixtral-8x7B-Instruct-v0.1"

pipe = pipeline(
    "text-generation",
    model=model,
    model_kwargs={"torch_dtype": torch.float16, "load_in_4bit": True},
)

messages = [{"role": "user", "content": "Explain what a Mixture of Experts is in less than 100 words."}]
outputs = pipe(messages, max_new_tokens=256, do_sample=True, temperature=0.7, top_k=50, top_p=0.95)
print(outputs[0]["generated_text"][-1]["content"])

<s>[INST] Explain what a Mixture of Experts is in less than 100 words. [/INST] A Mixture of Experts is an ensemble learning method that combines multiple models, or "experts," to make more accurate predictions. Each expert specializes in a different subset of the data, and a gating network determines the appropriate expert to use for a given input. This approach allows the model to adapt to complex, non-linear relationships in the data and improve overall performance.

Using Text Generation Inference

Text Generation Inference is a production-ready inference container developed by Hugging Face to enable easy deployment of large language models. It has features such as continuous batching, token streaming, tensor parallelism for fast inference on multiple GPUs, and production-ready logging and tracing.

You can deploy Mixtral on Hugging Face's Inference Endpoints, which uses Text Generation Inference as the backend. To deploy a Mixtral model, go to the model page and click on the Deploy -> Inference Endpoints widget.

Note: You might need to request a quota upgrade via email to api-enterprise@huggingface.co to access A100s

You can learn more on how to Deploy LLMs with Hugging Face Inference Endpoints in our blog. The blog includes information about supported hyperparameters and how to stream your response using Python and Javascript.

You can also run Text Generation Inference locally on 2x A100s (80GB) with Docker as follows:

docker run --gpus all --shm-size 1g -p 3000:80 -v /data:/data ghcr.io/huggingface/text-generation-inference:1.3.0 \
    --model-id mistralai/Mixtral-8x7B-Instruct-v0.1 \
    --num-shard 2 \
    --max-batch-total-tokens 1024000 \
    --max-total-tokens 32000

Fine-tuning with 🤗 TRL

Training LLMs can be technically and computationally challenging. In this section, we look at the tools available in the Hugging Face ecosystem to efficiently train Mixtral on a single A100 GPU.

An example command to fine-tune Mixtral on OpenAssistant’s chat dataset can be found below. To conserve memory, we make use of 4-bit quantization and QLoRA to target all the linear layers in the attention blocks. Note that unlike dense transformers, one should not target the MLP layers as they are sparse and don’t interact well with PEFT.

First, install the nightly version of 🤗 TRL and clone the repo to access the training script:

pip install -U transformers
pip install git+https://github.com/huggingface/trl
git clone https://github.com/huggingface/trl
cd trl

Then you can run the script:

accelerate launch --config_file examples/accelerate_configs/multi_gpu.yaml --num_processes=1 \
    examples/scripts/sft.py \
    --model_name mistralai/Mixtral-8x7B-v0.1 \
    --dataset_name trl-lib/ultrachat_200k_chatml \
    --batch_size 2 \
    --gradient_accumulation_steps 1 \
    --learning_rate 2e-4 \
    --save_steps 200_000 \
    --use_peft \
    --peft_lora_r 16 --peft_lora_alpha 32 \
    --target_modules q_proj k_proj v_proj o_proj \
    --load_in_4bit

This takes about 48 hours to train on a single A100, but can be easily parallelised by tweaking --num_processes to the number of GPUs you have available.

Quantizing Mixtral

As seen above, the challenge for this model is to make it run on consumer-type hardware for anyone to use it, as the model requires ~90GB just to be loaded in half-precision (torch.float16).

With the 🤗 transformers library, we support out-of-the-box inference with state-of-the-art quantization methods such as QLoRA and GPTQ. You can read more about the quantization methods we support in the appropriate documentation section.

Load Mixtral with 4-bit quantization

As demonstrated in the inference section, you can load Mixtral with 4-bit quantization by installing the bitsandbytes library (pip install -U bitsandbytes) and passing the flag load_in_4bit=True to the from_pretrained method. For better performance, we advise users to load the model with bnb_4bit_compute_dtype=torch.float16. Note you need a GPU device with at least 30GB VRAM to properly run the snippet below.

import torch
from transformers import AutoTokenizer, AutoModelForCausalLM, BitsAndBytesConfig

model_id = "mistralai/Mixtral-8x7B-Instruct-v0.1"
tokenizer = AutoTokenizer.from_pretrained(model_id)

quantization_config = BitsAndBytesConfig(
    load_in_4bit=True,
    bnb_4bit_compute_dtype=torch.float16
)
model = AutoModelForCausalLM.from_pretrained(model_id, quantization_config=quantization_config)

prompt = "[INST] Explain what a Mixture of Experts is in less than 100 words. [/INST]"
inputs = tokenizer(prompt, return_tensors="pt").to(0)

output = model.generate(**inputs, max_new_tokens=50)
print(tokenizer.decode(output[0], skip_special_tokens=True))

This 4-bit quantization technique was introduced in the QLoRA paper, you can read more about it in the corresponding section of the documentation or in this post.

Load Mixtral with GPTQ

The GPTQ algorithm is a post-training quantization technique where each row of the weight matrix is quantized independently to find a version of the weights that minimizes the error. These weights are quantized to int4, but they’re restored to fp16 on the fly during inference. In contrast with 4-bit QLoRA, GPTQ needs the model to be calibrated with a dataset in order to be quantized. Ready-to-use GPTQ models are shared on the 🤗 Hub by TheBloke, so anyone can use them without having to calibrate them first.

For Mixtral, we had to tweak the calibration approach by making sure we do not quantize the expert gating layers for better performance. The final perplexity (lower is better) of the quantized model is 4.40 vs 4.25 for the half-precision model. The quantized model can be found here, and to run it with 🤗 transformers you first need to update the auto-gptq and optimum libraries:

pip install -U optimum auto-gptq

You also need to install transformers from source:

pip install -U git+https://github.com/huggingface/transformers.git

Once installed, simply load the GPTQ model with the from_pretrained method:

import torch
from transformers import AutoTokenizer, AutoModelForCausalLM, BitsAndBytesConfig

model_id = "TheBloke/Mixtral-8x7B-v0.1-GPTQ"
tokenizer = AutoTokenizer.from_pretrained(model_id)

model = AutoModelForCausalLM.from_pretrained(model_id, device_map="auto")

prompt = "[INST] Explain what a Mixture of Experts is in less than 100 words. [/INST]"
inputs = tokenizer(prompt, return_tensors="pt").to(0)

output = model.generate(**inputs, max_new_tokens=50)
print(tokenizer.decode(output[0], skip_special_tokens=True))

Note that for both QLoRA and GPTQ you need at least 30 GB of GPU VRAM to fit the model. You can make it work with 24 GB if you use device_map="auto", like in the example above, so some layers are offloaded to CPU.

Disclaimers and ongoing work

• Quantization: Quantization of MoEs is an active area of research. Some initial experiments we've done with TheBloke are shown above, but we expect more progress as this architecture is known better! It will be exciting to see the development in the coming days and weeks in this area. Additionally, recent work such as QMoE, which achieves sub-1-bit quantization for MoEs, could be applied here.
• High VRAM usage: MoEs run inference very quickly but still need a large amount of VRAM (and hence an expensive GPU). This makes it challenging to use it in local setups. MoEs are great for setups with many devices and large VRAM. Mixtral requires 90GB of VRAM in half-precision 🤯

Additional Resources

• Mixture of Experts Explained
• Mixtral of experts
• Models on the Hub
• Open LLM Leaderboard
• Chat demo on Hugging Chat

Conclusion

We're very excited about Mixtral being released! In the coming days, be ready to learn more about ways to fine-tune and deploy Mixtral.