Hibernate Core 4.0.0.Beta1 has just been released. The complete list of changes can be found in JIRA release notes
As this is a Beta, we expect the API to be pretty much complete. At this point most of the work is going into the newly redesigned metamodel which is the representation into which Hibernate parses user provided metadata (XML and annotations) before building a SessionFactory. As we finish up that work in the coming weeks there may be adjustments to those contracts. However, most users will not leverage those contracts anyway.
As the redesigned metamodel is still being finished up and is currently likely to only work on simple domain models we have decided to delay removal of the org.hibernate.cfg.Configuration class and that method of building a SessionFactory until this work is done. So both approaches are available in parallel for the time being.