At least the GB200s OpenAI purchased have CX-8s, but it's very possible (perhaps even very likely) most of the millions of GB200s deployed PCIe 5.0 using CX-7s given the SuperMicro spec sheet.

Edit: found this SemiAnalysis post saying as much https://x.com/SemiAnalysis_/status/1947768988467138645/photo...

thanks! very interesting that they got a custom SKU.