The Dev has posted that Infinity will remain working and free until their paid subscription update is released. How they are achieving this I am unsure. The other reddit client I have installed, Stealth, which I just browse on anonymously, is still working also.

The Infinity dev says he’s working on a subscription version that is not ready yet.

There was another app developer doing that also (Boost? Not sure) and the developer said Reddit gave him and his users some grace period to get the new version out.