Graph API Web Hook for Group File

Hi guys:

I need to add web hook to group files and conversation using Graph API.

For conversation, it works well. But for files, it returns error:

{"error": {"code": "","message": "resource 'groups/86e5eb83-eb51-43ed-a73d-e2614bc86560/drive' is not supported.","innerError": {"request-id": "399c10e5-7f33-4f17-ba7d-443fb586b548","date": "2016-09-19T02:51:43"
    }
  }
}

The message means group file web hook is not supported yet, is this right? If it is, then when will it be supported? 

Any one knows this, please tell me the answer. Thanks.