I'm on Windows 10, Python 3.8.2 (but the same issue is happening on another machine with Windows 11, Python 3.7.3).

Running py -m pip install open-spiel==1.0.2 in a Windows Powershell terminal (both with and without administrator privileges) results in a legacy-install-failure error preceded by a subprocess-exited-with-error error. The full output is dumped here (note that Pastebin doesn't format this properly in the first window, so scroll down to the raw input at the bottom of the page).

One small locale footnote: [WinError 2] Het systeem kan het opgegeven bestand niet vinden translates to [WinError 2] The system cannot find the file specified.

I just upgraded from Windows 7 recently, exactly because the OpenSpiel installation required CMake and clang++. Now that I have those (as evidenced by the output), different errors arise. Is OpenSpiel's pip install not meant to work on Windows, perhaps?