Otto replaces Vagrant for the common use case: if you're just a person who wants to run a personal dev server, they'd like you to move onto Otto.

However, Otto is just a layer on top of Vagrant that automates a lot of the decisions that a dev would usually make. Vagrant is still relevant for other use cases, so they'll continue to develop it as a standalone product, too.

The biggest source of this confusion is the header of Otto's site - https://ottoproject.io/ - where it says "Meet the successor to Vagrant"

Not really; official statement from https://www.hashicorp.com/blog/otto.html:

> Vagrant is a mature, healthy project that is continuing to grow every day. We are committed to supporting Vagrant for the foreseeable future and will continue to release new versions. Otto is our vision for the next generation and will be developed alongside Vagrant.

> the successor to Vagrant https://www.hashicorp.com/blog/otto.html

So it does read like it was replaced but now we have some clarification. Vagrant will still be developed alongside of Otto.

Otto uses vagrant (as well as other hashicorp software) under the hood.