Do I have to upgrade to the latest OpenSSO Express build when it is released?
You do not have to upgrade to the latest build. You can stay on any build as long as you would like and upgrade to a future OpenSSO build or commercial release at any time, as long as your support contract is valid. Be aware though that, if you find an issue and need to contact the support team, upgrading to the latest build is the first thing they will ask you to do.