“ It will take a long time until any library code can safely adapt this new functionality since Python 3.9 will reach its end of life approximately in October 2

“ It will take a long time until any library code can safely adapt this new functionality since Python 3.9 will reach its end of life approximately in October 2025” Not true - for example, Black had been requiring python 3.6+ even before 3.5 and older were fully deprecated / unsupported. Just declare the minimum version your library requires in setup.py and let users decide.