I just installed GeoNetwork 3.2.1 The swagger documentation of the API stands "beta". When is the product release of the API going to be avalable ? I'm planning to use GeoNetwork exclusively from the API and the CSW service (not using the web interface). Should I use an older version of GeoNetwork in order to have a product release of the API ?
This should be asked on the mailing list better: http://geonetwork-opensource.org/community.html
We (developers of GeoNetwork) have no plan right now to "stabilize" the API or making it version "1.0". There are still many operations that are on the old non-REST API, so we will continue migrating and adding new services. Until we have a bigger set of operations that covers (almost) everything, I doubt we will change the version number.
An older version of GeoNetwork will not have the REST API, so I would never advise you to go back in time. That is a waste of time.
The thing is, even if it is a "beta" version, it is quite stable. Work being done right now is mostly migrating the old xml API to the new REST interface, ordering and standarizing input, output and namings. I would advise you to use it as is and forget about the number. The functionality behind the REST interface is mostly stable, the main work being done is just migrating the way of interacting with it (migrating to REST).