KDE Workspaces 4.11 has reached end of life and is no longer supported by upstream. It is therefore recommended for all users to upgrade to KDE Plasma 5.
A detailed upgrade guide is available [1], but in most cases it is enough to switch to the new desktop/plasma profile, update @world, and emerge kde-plasma/plasma-meta:
eselect profile list eselect profile set <target> emerge --ask --changed-use --newrepo --deep world emerge --ask --verbose kde-plasma/plasma-meta
If you normally use KDM to launch Plasma, note that it is no longer supported. Upstream recommends x11-misc/sddm instead which is pulled in by plasma-meta by default. OpenRC users should edit /etc/conf.d/xdm and update DISPLAYMANAGER. Systemd users should run: systemctl reenable sddm.service
Due to an an evolution of KDE upstream's release process [2], the traditional monolithic KDE 4 release is now split into three distinct components. This means that KDE Applications are now separate from the Plasma desktop and older KDE 4-based applications will continue to function as normal inside Plasma 5. KDE Workspaces 4.11 will remain in the tree for a reasonable time, but be warned that it is unmaintained and may cause conflicts with newer versions of KDE Applications.