I propose we leave ast.__version__ alone. Using ast.__version__ at all should be a very advanced usecase. Generally, you should just be able to look at sys.version_info. We could document this rather than duplicating sys.version_info in ast.__version__. I think ast.__version__ is mostly useful for things like:

print("Running with Python {} and AST {}".format(sys.mercurial[2], ast.__version__)