In rc3 sources for apt was added again (none were present in rc2). According to the release notes this is not a supported way to update packages?
vyos@vyos:~$ cat /etc/apt/sources.list.d/vyos.list deb http://dev.packages.vyos.net/repositories/current/vyos current main deb http://dev.packages.vyos.net/repositories/current/debian current main