JAX

JAX is "NumPy on steroids". It combines Autograd (automatic differentiation) with XLA (compilation). 2025 sees Flax NNX (PyTorch-style OOP) becoming standard.

When to Use

• TPU Training: JAX runs natively on Google TPUs.
• Research: If you need to compute 10th order derivatives or strange math.
• Massive Scale: DeepMind and OpenAI use JAX for training frontier models.

Core Concepts

Functional Transformations

grad(), jit(), vmap(), pmap().

Flax (NNX)

Neural network library. NNX introduces mutable state (OOP) to make JAX feel like PyTorch.

Statelessness

(Legacy Flax) parameters are stored separately from the model.

Best Practices (2025)

Do:

• Use jit: Always compile your functions.
• Use Flax NNX: Avoid the complexity of legacy immutable Flax/Haiku.
• Use shard_map: For distributed training across devices.

Don't:

• Don't use side effects: print() inside a jit function only runs once (during tracing).

References

• JAX Documentation