Yesterday, a new GCC 11.2.0, Glibc 2.34 & Binutils 2.37 based toolchain was uploaded. Unfortunately, something went wring with Glibc, and this new toolchain had to be removed.
If you ended up updating while on [build] the last 12 hours, your system will show a kernel error on booting and you will need to chroot into your install to downgrade.
See https://kaosx.us/docs/chrooting/ for chrooting.
pacman -Syu will show a lot of local packages newer then repo. After
pacman -Syu remove libxcrypt:
sudo pacman -Rdd libxcrypt
sudo pacman -Suu. Once all is downgraded it is safe to exit the chroot & reboot.