In at least the scientific python environment, there's "SPEC0" in which a lot of the de facto core libraries have basically agreed to support the last three versions of Python, no more.
For other libraries they can of course choose as they want, but generally I don't think it's so common for libraries to be as generous with the support length as cpython.
For other libraries they can of course choose as they want, but generally I don't think it's so common for libraries to be as generous with the support length as cpython.