In mid-March IK Multimedia sent out an email to AT4 CS users:
AmpliTube CS has been updated to version 5.0.2. This new version is permanently free for all IK users and offers a significantly improved workflow, upgraded sound quality and several new gear models.
AmpliTube 5 CS requires no additional purchases and will read all existing AmpliTube gear you own, along with any custom presets or other settings.
With this release, IK is ending support for AmpliTube 4 CS. We strongly encourage all users to upgrade to the new version for the best experience.
Similarly, since AmpliTube 5 CS offers the new Custom Shop 2, all future Custom Shop initiatives will only be available to AmpliTube 5 CS users. AmpliTube 4 CS users will still be able to access and restore their gear, but will not be able to purchase new models or access giveaways.
However, as you have noted some AT4 gear is not available in AT5. You can continue to use AT4
with your existing gear, but for new features and gear models you will need AT5 (paid-for or CS editions).
Some gear models, but happily no lives, were lost during floods in Italy, so they could not be remodelled for AT5.