As part of my morning fighting with Windows 10 Anniversary I learned something new. If vagrant can’t communicate with VirtualBox it will try to install the version it was tested with:

> vagrant up devel
==>  Provider 'virtualbox' not found. We'll automatically install it now...
     The installation process will start below. Human interaction may be
     required at some points. If you're uncomfortable with automatically
     installing this provider, you can safely Ctrl-C this process and install
     it manually.
==>  Downloading VirtualBox 5.0.10...
     This may not be the latest version of VirtualBox, but it is a version
     that is known to work well. Over time, we'll update the version that
     is installed.
     Progress: 100% (Rate: 590k/s, Estimated time remaining: --:--:--)
==>  Installing VirtualBox. This will take a few minutes...
     A couple pop-ups will occur during this installation process to
     ask for admin privileges as well as to install Oracle drivers.
     Please say yes to both. If you're uncomfortable with this, please
     install VirtualBox manually.

In my case it didn’t work because I already had a newer version of VirtualBox installed:

Vagrant has detected that you have a version of VirtualBox installed
that is not supported by this version of Vagrant. Please install one of
the supported versions listed below to use Vagrant:

4.0, 4.1, 4.2, 4.3, 5.0

A Vagrant update may also be available that adds support for the version
you specified. Please check www.vagrantup.com/downloads.html to download
the latest version.