It appears to have a cool-sounding JIT server mode, allowing multiple clients to share a caching JIT compiler which does most of the heavy-lifting:

https://www.usenix.org/conference/atc22/presentation/khrabro...

https://developer.ibm.com/articles/jitserver-optimize-your-j...

It also has a "dynamic AOT compiler", so first-run stuff can be JITed and cached for future execution instead of it all starting out interpreted every time.

The shared class cache was the thing I was thinking of, I think.

https://developer.ibm.com/tutorials/j-class-sharing-openj9/

Looks like maybe there is similar for OpenJDK & Oracle Java as of version 12 (I think it is?)

https://docs.oracle.com/en/java/javase/19/docs/specs/man/jav...