The changes that have been made to Open API are the following:
UML metamodel changes. UML 2.4.1 specification introduced few changes in the UML metamodel itself. Some metamodel classes were added, some of them were removed, some metaclasses properties were changed. Most of these changes are not in a core UML, so they will affect you if your plugin is oriented to complex things in UML. For the details of changes, see Supported UML Specification Changes from Version 2.3 to 2.4.1.