Interoperability between content management system and collaborative content system

A content management system and a collaborative content system implement interoperability features that allow a user to perform certain interactions with a collaborative content item via the interface of the content management system. For instance, the collaborative content system can outsource access permissions for the collaborative content item to the content management system. When the collaborative content system receives a user's request to access the collaborative content item, the collaborative content system requests permissions data for the collaborative content item from the content management system and then determines based on the permissions data whether to grant access to the user. The content management system can also outsource the account storage capacity for the collaborative content item to the collaborative content system. As a result, a collaborative content item that is stored in association with a user account on the content management system is not counted against the user account's storage capacity.