Honestly it's still kind of unknown. If you're billed directly through Hulu you get upgraded for free, but I can't find any information on if Hulu themselves will be hosting HBO Max content, or if it'll be like Apple where the distributor bills you for normal HBO and you use that login to access the HBO Max app. The press release from Warner gave absolutely no details.
That's the entire press release.
Before the Apple deal got confirmed as "Sign into the HBO Max app with your Apple ID" I would have said of course Hulu would be hosting it like they are right now, but now I'm less convinced.
So either way you'll get HBO Max, but it's not known where it'll be. To me this is why the lack of a deal with Amazon or Roku is so important. If it was streaming from Apple or Hulu then you could just download those apps on your Fire TV or Roku and it's no big deal, but since all those companies have made a big stink about AT&T not making a deal with them, that says to me that they want all Max content to be in their own app, with 50 different ways to log in, and not anywhere else.