This guide discusses migration from Hibernate ORM version 5.4 to version 5.5. For migration from earlier versions, see any other pertinent migration guides as well.
This version is very similar to Hibernate ORM 5.4; essentially it includes all bugfixes that have been applied to the 5.4 maintenance releases, and on top of this it introduces support for the Jakarta Persistence API (in addition the the JPA APIs we already support).
The implementation of Hibernate’s parsing of XML mapping definitions has been entirely reimplemented based on JAXB rather than DOM4J, making progress to remove this ancient dependency. No specific issues are known at this time.
The "enhanced proxies" feature has been introduced as a performance improving feature in 5.3 initially, at which time it was optional.
Since then, many more corner cases have been fixed and this feature is now always enabled. Enjoy the improvements! No changes are expected to be needed in user code to benefit from this.