It has a different part number and a "new" designation for the gearbox/bulkheads. A friend translated it for me and basically it says that they have been redesigned and reinforced to prevent the ring and pinion from losing mesh under high, sudden torque.
Just received a reply to my e-mail to HPI. Looks like the diff bearings are larger as well.
"Thank you for contacting HPI Racing and Hot Bodies customer service. It looks like we did change the bearing size on the new Savage Flux and we also changed the material on the diff as well to make them stronger. We also have changed the diff bulk head so all around the diffs are upgraded.
Michael | Customer Service
(:: PH 949.753.1099 x505/ FX. 949.753.1098
Toll Free: 1-888-349-4474
70 Icon, Foothill Ranch, CA, USA 92610"