Until now Hibernate tools "survived" that Hibernate 3.5+ could load hibernate 3 and 4 projects metadata without problems.

With JPA 2.1 this changed and it requires Hibernate 4.3+ to load these metadata.

We could update hibernate tools to use hibernate 4.3 to load the metadata but in doing so we would gain support for JPA 2.1 but at least loose support for loading Hibernate 3.3-4.2+ projects that uses custom user types (there could be more combinations that fails - figuring out how much requires a lot of work, but for now at least we know the usertypes are not binary compatible anymore).

To fix this a rethink/reimplementation is needed of how hibernate tools works.
It basicallly needs to become completely independent of hibernate binaries/classes.