"Fully titled the “AMD Ryzen Desktop Processor with Radeon Vega Graphics”, this new processor will utilize the same AM4 socket and motherboards that have been shipping since March of 2017."
AMD Ryzen 5 2400G and Ryzen 3 2200G APUs performance unveiled
AMD Ryzen 5 2400G with Radeon RX Vega 11 Graphics
For any particular existing motherboard it all depends on whether the motherboard manufacturer releases a BIOS update that supports the new Ryzen APUs. Until then we will have to wait and see. Since the Ryzen 5 2400G is supposed to be released on February 12 we shouldn't have to wait much longer.