Continuing with tradition, the AMD Chromebook is using Coreboot. Thus we have the first signs of it via Coreboot code review with this new Google board being codenamed "Kahlee." The Coreboot code began appearing for review just minutes ago after other Kahlee references in the Chrome OS world have been found in recent weeks.
This AMD Chromebook features two M.2 slots and is based on an AMD Stoney Ridge APU. AMD Stoney Ridge for the forgetful is their 2016 platform based on a 28nm process and using Excavator CPU cores with 3rd gen GCN graphics.
More details as they become available.