Imdb says episodes 12 and 13, the last two of the season.
IMDb - The Handmaid's Tale (2017– ) Full Cast & Crew
I read something like that, probably in the same article. Also that he was an economist and designed Gilead's economy?
I was so happy and so squicked simultaneously when I heard he was cast.
I have switched from hoping he won't play her Commander to hoping we won't have to watch a Ceremony.