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Facebook AI Research Sequence-to-Sequence Toolkit written in Python.
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Fairseq(-py) is a sequence modeling toolkit that allows researchers and developers to train custom models for translation, summarization, language modeling and other text generation tasks. It provides reference implementations of various sequence-to-sequence models, including:

Fairseq features:

  • multi-GPU (distributed) training on one machine or across multiple machines
  • fast generation on both CPU and GPU with multiple search algorithms implemented:
  • large mini-batch training even on a single GPU via delayed updates
  • mixed precision training (trains faster with less GPU memory on NVIDIA tensor cores)
  • extensible: easily register new models, criterions, tasks, optimizers and learning rate schedulers

We also provide pre-trained models for several benchmark translation and language modeling datasets.


Requirements and Installation

  • PyTorch version >= 1.0.0
  • Python version >= 3.5
  • For training new models, you'll also need an NVIDIA GPU and NCCL

Please follow the instructions here to install PyTorch:

If you use Docker make sure to increase the shared memory size either with --ipc=host or --shm-size as command line options to nvidia-docker run.

After PyTorch is installed, you can install fairseq with pip:

pip install fairseq

Installing from source

To install fairseq from source and develop locally:

git clone
cd fairseq
pip install --editable .

Improved training speed

Training speed can be further improved by installing NVIDIA's apex library with the --cuda_ext option. fairseq will automatically switch to the faster modules provided by apex.

Getting Started

The full documentation contains instructions for getting started, training new models and extending fairseq with new model types and tasks.

Pre-trained models and examples

We provide pre-trained models and pre-processed, binarized test sets for several tasks listed below, as well as example training and evaluation commands.

We also have more detailed READMEs to reproduce results from specific papers:

Join the fairseq community


fairseq(-py) is BSD-licensed. The license applies to the pre-trained models as well. We also provide an additional patent grant.


Please cite as:

  title = {fairseq: A Fast, Extensible Toolkit for Sequence Modeling},
  author = {Myle Ott and Sergey Edunov and Alexei Baevski and Angela Fan and Sam Gross and Nathan Ng and David Grangier and Michael Auli},
  booktitle = {Proceedings of NAACL-HLT 2019: Demonstrations},
  year = {2019},
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