I saw a comment on Reddit saying that Master Modes aren't even in Squadron 42 yet and aren't actively in testing. [Are they?]

They are in Squadron 42, they are actively in testing, they are working now.

Yes, and we've been testing this for months now. So it's been actively in the game. We've been playtesting ourselves on our own team, but it's also been put out there to the general studio as well. So we've definitely been in a really good feedback loop. We're really excited about that because the internal results for us have been really good and really positive.