Hi @Delantonio ,
having searched the mainboard documentation I suppose it to be 3rd gen, but it´s definetely not pointed out clearly.
Talking about PCIe: This has nothing to do with your question, but keep in mind, that the two M.2 slots available on your Z370 mainboard do not support all M.2 SSD types. The image below shows the two connectors mentioned in detail.
Cheers
Major ToM
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