It will be similar to how the SponsorBlock “chapters” feature was handled, except also having a system for some people to get free access as well (most likely after waiting some time, or going through some queue of people wanting free access)
Chapters on SponsorBlock are now free, but on release, were behind a paywall on the extension only. It’s simply a boolean that changes client side that enabled the functionality, so adds no privacy implications that an authenticated API would. The API is still free for others to implement with, such as on alternative clients, and in theory you could build the extension with the check commented out of course.
It’ll most likely be priced the same as chapters was (5$) with past donators automatically getting free access. But I might choose a lower price too depending on how it goes.
So it’ll just be a client side flag on the extension itself.
What if you bought an android phone, and could ask them for the source code to the Linux kernel on it, but if they caught you sharing it online, they would not allow your phone to update to the latest Android version?