AMD won’t be supporting PCIe 4.0 on older Ryzen motherboards. These include the budget-oriented A320 and B450, as well as the higher-end X370 and X470 boards. PCIe 4 is the successor to the present third-gen standard and will deliver up to two times as much bandwidth compared to its predecessor. However, unless you haven’t pre-ordered one of the latest cutting-edge X570 motherboards, you won’t be able to take advantage of it.
Robert Hallock, one of the Ryzen product managers confirmed this on Reddit:
Although some motherboards especially Gigabyte’s X470 offerings were looking to support PCIe 4, looks like AMD has put a quick end to that idea. To avoid confusion or any technical difficulties, the company has made the decision to support the new standard only on the third-gen Ryzen chipsets.
In my opinion, this still isn’t a deal breaker, and if you have an older X470 board, I don’t see any reason for you to splurge for the newer X570. Firstly, there aren’t any GPUs in the market right now which support PCIe 4.0, and even if AMD’s Radeon RX 5700 lineup does support it, don’t expect much of a performance uplift except in very specific applications. Most games are barely able to saturate the PCIe 3 standard even now, so the advantages of PCIe 4 won’t become apparent anytime soon.