Site Navigation with versions

We have 2 versions of our product, with correlating documentation. One of them has API Reference and the other does not. I want show API Reference in the Top Navigation bar on Version 1, but not on Version 2. How do I do that?

When I remove the API Reference link on dash.readme.com/project/<project_name>/v1.0/usability, it is also removed from dash.readme.com/project/<project_name>/v2.0/usability. I would expect separate behavior, since the version number is in the URL.