At the current state, pr0gramm's API is considered unstable and is not versioned. However, we try to avoid large breaking changes but cannot give any guarantee that it won't happen. You can join our Discord Server and get notified on when are about to deploy breaking API changes. Our discord community is open for everyone who wants to develop anything that has to do with pr0gramm and/or uses the API. Bots, services, User Scripts; you name it.
pr0gramm.com supports OAuth 2.0 using Grant Code Authorization to do API requests. You can use this to provide a "Log in with pr0gramm" experience for your application as well as accessing API endpoints with user credentials without needing their password.