Working upon the premise that the suggestion of denoting certain APIs as incubating/experimental bears some merit:
The API can be roughly divided into two surfaces: the stable surface, and the unstable surface.
The stable surface is the API which is known to be stable; outside of bug fixes, there should be little to no changes in this API which would cause a mod compiled against it to be broken, behavioral-wise or binary-wise. (In old Forge terms, the API after a Recommended Build would be considered to be wholly on the stable surface.)
The unstable surface is the API which is not stable, and therefore is subject to change or removal over the coming versions. Mods using APIs on the unstable surface may or may not work when built on newer versions.