BIOSTAR formally (officially) enabled PCI-Express gen 4.0 support for four of its socket AM4 motherboard models based on the AMD X470 and B450 chipsets, through BIOS updates. The updated BIOS lets you use PCI-Express gen 4.0 graphics cards on the topmost PCI-Express x16 slot, and the M.2 NVMe slot that's directly wired to the AM4 SoC. The expansion slots that are wired to the chipset are still restricted to PCIe gen 2.0. You will need a 3rd generation Ryzen 'Matisse' processor for PCI-Express gen 4.0. Among the motherboards that receive PCIe gen 4.0 support through BIOS updates are the AB45C-M4S (B450MH), the AB35G-M4S (B45M2), the AX47A-A4T (X470GT8), and the AX47A-I4S (X470GTN). The links lead to the BIOS image files on BIOSTAR website, which you use at your own risk.