BREAKING NEWS: JAX NVIDIA GPU & XLA: GPU's biggest customer just announced that they have dropped JAX GPUs and would…

SemiAnalysis Twitter · SemiAnalysis (@SemiAnalysis_) · 2026-05-30

xAI, reportedly NVIDIA's largest JAX customer, has abandoned JAX on GPUs and is replacing it with a custom C-based training framework built with Grok Build, after its JAX stack reportedly achieved MFU below 10%.

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NVIDIA GPU Ecosystem Performance Gaps: JAX Dropout, Blackwell Regression, and Kernel Utilization

Extraction

Topics: xaijaxnvidia-gputraining-infrastructuremfu

Claims

xAI has dropped JAX on NVIDIA GPUs in favor of a custom C training framework built with Grok Build.
xAI's JAX-based training stack reportedly achieved model flops utilization (MFU) below 10%.
NVIDIA's JAX team has been under intense pressure to resolve performance issues for xAI.

Key quotes

GPU's biggest customer just announced that they have dropped JAX GPUs and would rather vibe code an C training framework with Grok Build.

Reportedly xAI's JAX stack had MFU lower than 10%.