Thinking a bit more about this, if the intended class is org.hibernate.jpamodelgen.test.innerclasses.WorkOrder$WorkOrderId_ (and I think it should be per definition), I don't think metamodel generation works. I would need to add WorkOrderId_ to WorkOrder itself, which is not possible. TBH, I don't think that this inner class use case can be implemented using the current definition of a canonical metamodel class.