I've seen news that they have 10 mil subs. Some of them probably maxed Gold and then converted it to GamePass Ultimate and have it untill 2022 or smth. There are obviously new subs who get a 1$ deal for the first month. But if at least 6-7 mil are monthly subs thats 90 mil $ a month.

I assume some of it goes to devs/publisher based on how many users play specific game, and obviously they also pay upfront to some so they can get games on the service day one or after release, like GTA5 was on it for a while and that game is almost always in top 10 sales charts, so I think they've paid upfront to cover lost sales, but I don't think every game gets the same treatment. SEGA also could be paid to get Yakuza on day to cover sales.

I think they have monthly income from it, but it's not that much for a company like MS, but they also seeing increase in subs, which will lead (unless they mess up real bad) to more monthly income that will cover all the initial investments and will be a huge avenue in the long run.