Hyrum's Law

If

With a sufficient number of users, every observable behavior of your system (even bugs) will be depended on by someone.

Then

"Internal" doesn't exist once you have users. Version and feature-flag what you promise; deliberately vary what you do not, so nobody can build on it in the first place.

Unless

Deliberate Variance — if every observable behaviour were sacred nothing could ever change, so vary what you never promised — randomised iteration order, planned outages — and the dependency never forms