Chris Lattner: Legendary compiler engineer who created LLVM, the Clang compiler, and the Swift language, led key work on TPUs at Google and Autopilot software at Tesla, and now co-founded Modular to build a new full-stack AI infrastructure and the Mojo programming language.
What this episode covers
Lattner walks through Mojo, a new programming language designed as a full superset of Python that adds systems-level features so code can run from interpreters to GPUs and AI accelerators without a rewrite. He explains how Mojo achieves massive speedups by moving from CPython's interpreter to a compiler, dropping boxed objects into registers, adding optional types, value semantics, ownership, and auto-tuning. The bigger picture is Modular's mission to unify the fragmented AI stack so models don't need to be rewritten in C++ or hand-tuned with CUDA kernels for every new chip. He recounts hard-won lessons from launching Swift and from the painful Python 2-to-3 migration, shaping his deliberate, community-driven, no-fragmentation approach to releasing Mojo. The conversation closes on the future of programming, LLMs as coding companions, and making AI accessible to far more people.
No purchasable items were genuinely recommended in this episode.
Big reveals from this episode
- Lattner claims Mojo code has demonstrated over 30,000x (up to 35,000x) speedups over Python.
- He bluntly argues that people who prefer curly braces over indentation 'are just wrong.'
- Reveals he left Apple in January 2017 specifically to go work on AI, ending up at Google on TPUs.
- Admits his earlier Swift-for-TensorFlow project 'did not work out super well' because Swift isn't Python.
- Tells the story of Swift's stressful, buggy 2014 launch as the reason he deliberately released Mojo as a rough 0.1.
- Says he doesn't spend time worrying about Skynet because 'if Skynet takes over and kills us all then I'll be dead.'
- Credits Jeremy Howard as the person who pushed him for years toward building Mojo: 'Chris finally listened to Jeremy.'
Worth remembering
- Mojo can use the fire emoji as a file extension, which Lattner calls one of the first emojis ever used that way.
- Mojo's compiler embeds an interpreter, letting it run Python-style dynamic metaprogramming at compile time.
- CPython boxes every integer as a heap object with reference counting, which is tightly intertwined with Python's GIL.
- Mojo gained over 10,000-11,000 Discord members within roughly two weeks of release.
- Over 70,000 people signed up for the Mojo Playground in the first two weeks, about one person per minute.
- When Swift launched at WWDC, only about 250 people at Apple even knew the project existed.
- Jeremy Howard and a researcher beat Google in the DAWNBench ImageNet training competition using progressive image resizing rather than brute-force compute.
- Mojo was only about seven months old at the time of the interview and still lacks classes, lambda syntax, and list comprehensions.
- In C++, throwing a 'zero-cost' exception can be roughly 10,000x more expensive than a normal function return.
- Lattner argues Excel is arguably the most popular programming language in the world.