As you can see by the version numbers Guzaba CMS is still not considered ready for the prime time and some of the APIs may change. On the other hand it is developed for an year already and the Security Model got updated recently (in the 0.6 branch) to a Hierarchical RBAC so no major changes are expected there - only additions (like SoD) and improved and enriched user interface (role capabilities). The most important framework classes like these implementing the Active Record and the MVC patterns are also quite stable. Some changes are expected in the exceptions though. All this is to say that even it is far from being "stable" in developers sence once the interface is stablelized and is tested for some time more it can be considered a finished product.
For information on what functionality is planned to be added a roadmap is provided. Please note that Guzaba CMS is not a sponsored project at this time and the specified timeframes may not be observed. For the history of the added/changed features and fixed major bugs you can consult the changelog.