setuptools.Extension used to be able on Linux with GCC automatically distinguish whether the code is a pure C or C++ and link accordingly. It seems to me that with either Python 3.14.6 something broke and I had to add patches like fix build failure with Python 3.14 by linking libstdc++ by mcepl · Pull Request #85 · SethMMorton/fastnumbers · GitHub to have C++ linking working. Is it a regression or we did screw up something in openSUSE?