Musk: xAI's pretraining runs on in-house C/C++ stack, RL stack still legacy mess
jsuarez · x · 2026-09-14
Elon Musk revealed that xAI's pretraining software now runs on an internally developed C/C++ stack, written primarily by the Starlink software team and "probably best in industry," while the reinforcement learning stack remains a legacy patchwork of third-party systems awaiting a rewrite. A reply recommends PufferLib, a fast 100% CUDA C RL stack for small models, noting its design tricks are useful even for non-LLM workloads.
Related event: Musk Says xAI's C/C++ Training Stack Is Still Human-Written(2 posts)→
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