On first looking into JAX :: Giles' blog
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On first looking into JAX
Posted on 30 May 2026
in
Python,
AI,
Musings
Much have I travell'd in the realms of gold,
And many goodly states and kingdoms seen;
Round many western islands have I been
Which bards in fealty to Apollo hold.
Oft of one wide expanse had I been told
That deep-brow'd Homer ruled as his demesne;
Yet did I never breathe its pure serene
Till I heard Chapman speak out loud and bold:
Then felt I like some watcher of the skies
When a new planet swims into his ken;
Or like stout Cortez when with eagle eyes
He star'd at the Pacific -- and all his men
Look'd at each other with a wild surmise --
Silent, upon a peak in Darien.
John Keats, On First Looking into Chapman's Homer
I've been working with PyTorch quite a lot for the last couple of years, and feel<br>like I've come to a reasonably solid understanding of how it all fits together.<br>Working through Sebastian Raschka's book<br>"Build a Large Language Model (from Scratch)",<br>training my own LLMs locally and in the cloud,<br>rebuilding Andrej Karpathy's 2015-vintage RNNs --<br>over time, it all adds up!
But, of course, there are other frameworks, and one I kept hearing about was<br>JAX. While it's less<br>dominant than PyTorch, it has a reputation for a certain cleanliness, a certain purity.<br>And having spent time over the last couple of weeks working through the tutorials, and translating small PyTorch examples<br>into it, I've been really impressed.
In this post I want to give an overview -- to report back to beginners like me, still<br>living in PyTorch-land, on my new discovery. Less like Herschel discovering Uranus,<br>and more like a 16th-century European coming back after having discovered something that<br>the people who lived there were perfectly well aware of. What is this JAX thing,<br>and how does it differ from PyTorch?
Some theses, significantly overstated
I think that the main differences between PyTorch and JAX are something like this, but a little<br>less strident:
PyTorch is engineering; JAX is maths.
PyTorch has...