3.15 makes UTF-8 the default for I/O; previous versions require an option to open() to read/write UTF-8. C++23 adopted UTF-8 as the only portable source code file format.

Backwards compatibility is a serious impediment to changing code and APIs using UTF-16 to use UTF-8, but this is happening. In May 2019, Microsoft added the capability for an application to set UTF-8 as the "code page" for the Windows