Q: Does GCC support C++20 std::format? If it doesn't, do you know what compiler or version will?
See cppreference/format.

A: It's 2023 Now! Cheers!
GCC 13, CLANG 14 and MSVC 16.10/VS 2019 all have the {fmt} based std::format available in respective standard libraries.
Hopefully we'll have C++23 std::print available soon.

See Compiler support here :-

*

*gcc (libstdc++)

*clang (libc++)

*msvc (vc++)

A: Now libstdc++ has implemented it!
https://gcc.gnu.org/pipermail/libstdc++/2022-November/054991.html

A: 
Does gcc support C++20 std::format?

Not yet!
There's no compiler support yet, not even gcc 11. See Text formatting in Library features.
Compiler support for C++20 library features

A: GCC 13 has added support for std::format.  According to cppreference, as of GCC 13, no gaps remain in its C++20 support (in both the core language and the standard library).
This bugzilla ticket notes that some C++23 extensions to std::format have not yet been implemented.
GCC 13 can be expected around April 2023.
The GCC trunk installation on compiler explorer includes std::format support.

A: As of today (November 15, 2022), GCC 12.2 does not support this feature. Or rather, its standard library implementation doesn't support it (cause it's a library feature, not the compiler-one).
NOTE: The feature is mentioned as implemented in GCC 13.0 (link)
You can try Clang 14.0.0 and upward for now, but note following:

In libc++ of Clang 14.0.0 std::format support added but: "The paper is implemented but still marked as an incomplete feature. Not yet implemented LWG-issues will cause API and ABI breakage" (link)
In libc++ of Clang 15.0.0 and later, this feature can be enabled with the -fexperimental-library compiler flag (link)

Also you can try MSVC 16.10 and upward. Support of std::format is mentioned as complete.

Standard library current status can be seen here:

*

*GCC: libstdc++


*Clang: libc++


*MSVC: msvc-170
