Parallax

Parallax is a library for automatically scaling JAX models. It simplifies the process of training large models by offering automatic parallelism strategies and memory optimizations, allowing you to focus on your model architecture rather than sharding configurations.

Parallax helps you:

• Automatically shard your JAX models and functions without manually defining PartitionSpecs.
• Apply advanced parallelism strategies like Fully Sharded Data Parallel (FSDP) and Distributed Data Parallel (DDP) with ease.
• Optimize memory usage through model offloading (keeping weights in CPU RAM) and rematerialization.

With Parallax, you can scale off-the-shelf JAX models to run on larger hardware configurations or fit larger models on existing hardware without extensive code modifications.

This is not an officially supported Google product. This project is not eligible for the Google Open Source Software Vulnerability Rewards Program.

Installation

You can install Parallax using pip:

pip install google-parallax

Usage

Parallax integrates seamlessly with Flax NNX models. Here is a simple example of how to use auto-sharding:

import parallax
from flax import nnx
import jax
import jax.numpy as jnp

model  = parallax.create_sharded_model(
    model_or_fn=lambda: Model(...),
    sample_inputs=(jnp.ones((1, 32)),),
    strategy=parallax.ShardingStrategy.AUTO,
    data_axis_name='fsdp',
    model_axis_name='tp',
)

Features

• AutoSharding: Automatically discover optimal sharding strategies.
• FSDP & DDP: Ready-to-use implementations of common parallel training strategies.
• Model Offloading: Stream model weights from CPU to device memory to train larger models.
• Rematerialization: Automatic activation recomputation to save memory.

Contributing

We welcome contributions! Please check docs/contributing.md for details on how to submit pull requests and report bugs.

Support

If you encounter any issues, please report them on our GitHub Issues page.

Citing Parallax

To cite Parallax please use this citation:

@software{parallax2026,
  title = {{Parallax}},
  author = {Carpenter, Jeff and Yan, Stella and Liu, Dangyi and others},
  year = {2026},
  url = {https://github.com/google/parallax},
}