Not that recent, the switch has been there since 2.2 alpha 2, released 8 years ago (August 22, 2001):

    __all__ = ['all_feature_names', 'nested_scopes', 'generators', 'divisi...
    absolute_import = _Feature((2, 5, 0, 'alpha', 1), (2, 7, 0, 'alpha', 0...
    all_feature_names = ['nested_scopes', 'generators', 'division', 'absol...
    division = _Feature((2, 2, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 8192...
    generators = _Feature((2, 2, 0, 'alpha', 1), (2, 3, 0, 'final', 0), 0)
    nested_scopes = _Feature((2, 1, 0, 'beta', 1), (2, 2, 0, 'alpha', 0), ...
    print_function = _Feature((2, 6, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0)...
    unicode_literals = _Feature((2, 6, 0, 'alpha', 2), (3, 0, 0, 'alpha', ...
    with_statement = _Feature((2, 5, 0, 'alpha', 1), (2, 6, 0, 'alpha', 0)...