I've seen some use a versioned media typed like GitHub [0] or add a version parameter like "vnd.example-com.foo+json; version=1.0" [1]. People may use this version for the entire API or for versions of that specific resource as well.

[0] https://developer.github.com/v3/media/ [1] http://blog.steveklabnik.com/posts/2011-07-03-nobody-underst...