Version 5.x currently uses a subset of the data layer variables available from the 4.x libraries. All the previous variables, however, can be left in your Data Layer as future 5.x optional classes and updates will make use of them.
Version 5.x uses a completely different set of APIs to set it apart from version 4.x. The two main differences are:
Multiton instance requiring an instance key, replaces the singleton instance call
Event and view change calls replace the single track call
// version 4.x & prior
// version 5.x
[Tealium instanceForKey:@"testInstanceID"] trackEventWithTitle:@"buttonClick"
[Tealium instanceForKey:@"testInstanceID"] trackViewWithTitle:@"mainView"
// Note: An event or view title is required, but dataSources are still optional