Python 3.15 arrives with lazy imports and upgraded experimental compiler

Python released stable version 3.15.0 on October 9, adding explicit lazy imports for faster startup and changing the default text encoding to UTF-8. Official macOS binaries now install support for running threads without the interpreter's global lock by default, while Windows 64-bit binaries use the tail-calling interpreter. The release notes report a 7-8% geometric mean performance improvement for the experimental just-in-time compiler on x86-64 Linux over the standard interpreter. They also warn that IDLE and other applications using the tkinter graphics module may hang when opening certain dialogs on macOS 27.0, an issue believed to affect all current Python versions.