The process defined at https://www.zabbix.com/documentation/4.0/manual/installation/upgrade/packages/debian_ubuntu includes zabbix-release_4.0-1+stretch_all.deb but this installs 4.0rc3 from the 3.5 repo. 

There is a file on the repo called zabbix-release_4.0-2+stretch_all.deb but this isn't mentioned in the documentation so not sure if I should use it. 

Please could the documentation be clarified? 

I tried to upgrade from 4.0rc3 to 4.0.0 but then I got into the trap of https://support.zabbix.com/projects/ZBX/issues/ZBX-14940 so ultimately I just went back to 3.4