v5 can load your llblgenproj project and generate code for it but it will be v5 generated code which might require you to migrate your own code a bit. Any person who buys v5 can get a free v4 or v3 license if they want, so if you buy v5 and want to continue working in v4, that's fine, we'll send you a v4 license free of charge in that case and you can download v4 from the website in that case.