Despite AMD not supporting the PCIe 4.0 standard on pre-X570 motherboards, Biostar has gone ahead and activated the functionality on four of the brand's AMD 400-series motherboards.
Like Asus' case, Biostar can only offer the PCIe 4.0 speeds on the main PCIe x16 and M.2 slots. However, Biostar didn't specify whether the PCIe x16 slot will operate at x16 speed or limited to x8 with PCIe 4.0 enabled.
While the option to switch on PCIe 4.0 might be available now, AMD will eventually disable it in an AGESA microcode update. Basically, if you want PCIe 4.0, you'll be stuck on the same firmware for the rest of the motherboard's lifespan and miss out on any future features, performance enhancements or bug fixes. That's the price you'll pay if you pair a Ryzen 3000-series chip with a 400-series motherboard and expect PCIe 4.0 support.
Biostar has a bunch of AMD 400-series products in its arsenal, but only four made the cut. The X470-based motherboards include the X470GT8 and X470GTN while the B450-based offerings consist of the B450MH and B45M2. The firmware to enable PCIe 4.0 is available for download at the motherboards' respective product pages.
Now that Asus and Biostar have thrown the first stones, it'll certainly be very interesting to see whether other major motherboard vendors, such as ASRock, Gigabyte and MSI will jump on the bandwagon.