What do you mean when you say API? Other northbound interfaces? APIs like maapi or cdb?
Unless you have used the special hide-group full only CLI and WebUI is hidden. Other northbound interfaces, NETCONF, REST and SNMP are still accessible.
Hide-groups’s never hide APIs like maapi or cdb.
If you have trouble making it work, remove the hide-group, make sure you can access everything you want from the APIs, add the hide-group again, it should still work.
For more information see section 10.7 Hidden Data in the User Guide.