During the long pandemic hiatus, Hader and his writing partners were able to complete writing on Season 4. But since filming had yet to begin on Season 3, they were able to go back on rewriting that season using the Season 4 scripts -- even though HBO has yet to order a fourth season. "We mapped out Season 4 and then went back and started laying stuff in Season 3 that could be in Season 4 and it was really helpful," he tells Collider. "It was kind of like a great way of, I mean Season 3, we end up kind of fully overhauling a lot of elements of it because we had written four. So it was good.” Meanwhile, Hader says he expects Barry Season 3 to air early next year.