Assuming it flies soon, it will be the largest aircraft to date to use hydrogen for part of its power. The engine doesn't burn hydrogen directly. The hydrogen is used by a fuel cell that generates electricity to run an electric motor that turns the prop. The fuel cell and motor are both in the nacelle. For now, a tank of compressed hydrogen in the fuselage will provide the fuel but the company is also developing liquid hydrogen pods that will allow relatively convenient supply of fuel to the operational aircraft. That system is still in development. The ultimate goal for the system is a retrofit for ATR72 turboprops.
This is a companion discussion topic for the original entry at https://www.avweb.com/aviation-news/faa-clears-partially-hydrogen-powered-flight