I have refactored the API to no longer require Javassist and moved all Javassist implementations to a designated package. Finally, I have exposed the Enhancer via the BytecodeProvider and read it from there at all relevant places. I still need to polish it a bit but will publish my solution on my fork tomorrow.

As a next step, I would create components for everything done in Javassist with Byte Buddy which would later need to be assembled to replicate the functionality. Once I am done with this, I would probably need some help. Is there a better channel then a JIRA issue for this? Can I join some Slack channel for discussing things with the interested people?

As for compatibility: I am doing my best to avoid incompatible changes and Byte Buddy has not had too many incompatible changes after the 1.0 release. But in the nature of byte code, incompatible changes happen as the byte code format is itself not backwards compatible. As any byte code generation library is to some extend a reflection of the byte code format, it is not always possible to follow through. Also, if a feature is quite new, I sometimes need to change it. I sometimes develop a feature for a customer and publish it along the way. If I notice a severe performance problem, for example, I rather sacrifice compatibiility. Mature features do not typically change much and I think it would be those features that Hibernate would use the most.