With the ISO release announcement, KDE 4.12.0 is also becoming available for all KaOS regular repositories users.
Not only KDE 4.12.0 is part of your next update, for most users more than half their install will be replaced by a newer kernel, xorg stack among the many updates.
It is always important to check if your mirrors are synced before attempting an update, but with these kinds of updates, it cannot be stressed enough, run:
mirror-check
either in the terminal or start the mirror-check app, and make sure all is 100 % synced before running
sudo pacman -Syu
If your mirror is not synced give it about two hours, then try again.
It is also better for these kinds of updates not to use Octopi, but run pacman -Syu directly.
