The Pittsburgh Steelers currently have four quarterbacks on their 90-man roster. Only three will be carried on the 53-man roster once the regular season begins, but it’s not impossible that a fourth is kept on the practice squad now that it has expanded to 16 players–regardless of the discussion of whether or not there are enough reps to go around to justify it.
Will they do that? I don’t know. But it would have to start with all four of them proving that they deserve to be on the team. We can safely project that Mitch Trubisky and Kenny Pickett are going to be on the team, but who is going to be the third quarterback?