GCC 11 Aims To Default To C++17 Standard
As it stands now C++14 is the default C++ standard when compiling with GCC and not specifying an alternative -std=. But for GCC 11 they are planning to bump that to the next revision, C++17. Technically there still would be time to make this change for GCC 10, but it's getting late into the cycle without much time for addressing any fallout that may arise.
As such, discussions this week put the proposal to change the default to -std=gnu++17 (the GNU dialect of C++17) once GCC 11 opens.
GCC 10 "stage one" feature development meanwhile is ending in two weeks. GCC 10 stable should be out in Q2'2020 while GCC 11 will be out in early 2021. The state of C++17 as well as the yet-to-be-released C++2A (C++20) for the GCC compiler can be found on their standards support page.