I myself just got finished upgrading a huge project with about half a dozen apps and a few shard projects, from Grails 4 to 5, and it wasn't that bad. I expect that upgrading to Grails 6 will be about the same, as it is mostly a dependency upgrade and the CLI rewrite. Grails 7 on the other hand will probably be more disruptive because it involves upgrading to Spring Boot 3.x, which forces Java 17, and I think it pushes Hibernate 6 because of depdencies, which will require overhauling Gorm because Hibernate 6 removed the criteria query API. Plus there is Groovy 4, or maybe 5 depending on the release date and how hard it is to upgrade. Grails 7 will also probably remove the navigable Map for config, which could force a lot of plugins to be updated, or not work in Grails 7. All those dependency updates have the potential to break a lot of stuff and cause a fair amount of work for the Grails team. I'm sure they will also upgrade Gradle which is always a fun time, probably for them and us on the other side. We'll have to see how things progress.