The first release candidate for GCC 15.1 is available from https://gcc.gnu.org/pub/gcc/snapshots/16.1.0-RC-202523/ ftp://gcc.gnu.org/pub/gcc/snapshots/16.1.0-RC-20250423/
and shortly its mirrors. It has been generated from git commit r16-8809-g9fa782dee8894e01. I have so far bootstrapped and tested the release candidate on x86_64-linux. Please test it and report any issues to bugzilla. If all goes well, we'd like to release 16.1 on Thursday, April 30th.
