PyThaiNLP published the first version is 0.0.4 to PyPI at 6 years ago, so PyThaiNLP 4.0 will have special codename. The codename for PyThaiNLP 4.0 is PyThaiNLP 4.0 (Real).
See 4.0 Milestone.
Report bug: https://github.com/PyThaiNLP/pythainlp/issues
If you want to contribute to PyThaiNLP, you can read Contributing to PyThaiNLP.