As of August 17th, 2015 Gentoo has officially made the transition from cvs to git as the version control system (VCS) for the Gentoo ebuild repository. It is now possible to start using git and some post repository hooks to sync the main ebuild repository directly from the GitHub mirror.
Make sure Portage is at the latest stable version (at least >=2.2.20), then update the system's gentoo.conf with the following content:
[DEFAULT] main-repo = gentoo [gentoo] location = /usr/portage sync-type = git sync-uri = git://github.com/gentoo/gentoo.git auto-sync = yes
Setup post sync hooks to pull in news, metadata, etc. These originate from different repositories and are integrated into the rsync mirrors. Since rsync is not being used in this case, they must be manually synced as well.
Nuke the old Portage files:
rm -rfv /usr/portage/* /usr/portage/.*
Finally, sync the system using the emerge command: