Microsoft Azure ND v2 Largest Stated is a large GPU cluster operated by Microsoft, located in the United States, in the private sector. It came online around November 2019. At that moment it ranked number 31 among known clusters.
It is built on 800 NVIDIA V100. That amounts to about 50.53 H100e of AI compute. The cluster draws roughly 0.53 MW. Its hardware is estimated at $16M.
Epoch AI rates the certainty of this record as confirmed. This was the largest size mentioned. There were likely smaller ones as well, and possibly multiple of this size