The new Xray X12 comes with a steel/carbon axle. Its a steel rod inside the axle. Looking forward to see how i works (i think)
Edit: when looking at the presentation on the Xray site, in one place it mentiones "Newly-designed rear differential has a new way of combining the steel axle with the graphite axle for increased durability", while on another place it says "Super-lightweight rear axle made from 1-piece high-grade graphite rod, additionally precision hand ground to eliminate vibration and run-out".
When I asembeled the car, the axle felt quite heavy.