Stone to Silicon

Artificial intelligence · July 2025

Grok 4

xAI scales reinforcement learning on a 200,000-GPU cluster.

xAI trained Grok 4's reasoning with reinforcement learning on its 200,000-GPU Colossus cluster in Memphis. Grok 4 Heavy was the first model to score 50.7% on the text-only Humanity's Last Exam, and it reached 15.9% on ARC-AGI-2.

See it in the living treeWikipediaSource

Arcs above join it to what it stood on, arcs below to what it led to. The bar places this stretch on the tree's whole timeline.

What it built on 2

Related measurements

The dashed line marks when it first worked.

Best AI score on GPQA Diamond Latest: 95.8 % correct (2026) Source: Epoch AI, Capabilities & benchmarking (benchmark_data.zip, gpqa_diamond.csv); Anthropic: Claude 3 public launch (March 4, 2024)

Training compute of notable AI models Source: Epoch AI, Notable AI Models (CC BY 4.0)

ML hardware FLOP/s per dollar Source: Epoch AI, ML hardware (CC BY 4.0)