There are plans to build libgraal in JDK master using a version of Native Image running on a JDK one version behind JDK master. This Native Image execution needs to be able to load the JVMCI classes as they are built into the libgraal image. As such, the JVMCI classes must have a class file major version of N-1 where N is the major class file version of JDK master.

A concrete example that makes this clear(er):

The class file major version number in JDK 26 will be 70[1]. The class file major version for the jdk.internal.vm.ci classes in JDK 26 needs to be 69.

[1] https://bugs.openjdk.org/browse/JDK-8355793