Tim, to add to what Seth mentioned, the documentation is actually referring to the Vagrant API version. Early Vagrant versions used a 1.0 or lower version, after around Vagrant 1.2 or so they revamped the entire API but maintained most of the backwards compatibility, but the API version is a flag now inside the Vagrantfile. You are correct that synced_folders did change, but unless you were coming from a pre-1.0 Vagrant or hadn't used 'vagrant init' with a recent version of Vagrant, you should have been using V2 all along.