Comment by ziotom78

I believe they are really referring to the default mode used by GCC when no standard is explicitly stated.

The email mentions that the last time they changed it was 5 years ago in GCC 11, and the link <https://gcc.gnu.org/projects/cxx-status.html#cxx17> indeed says

> C++17 mode is the default since GCC 11; it can be explicitly selected with the -std=c++17 command-line flag, or -std=gnu++17 to enable GNU extensions as well.

which does not imply a change in an obscure feature (bootstrapping) that would only affect a few users.