KSCHAHN is right, Group III_ does not appear in API Annex, but the VI is much higher than is required for Group III and several other folks use the Group III+ designation
Dexos Gen 3 costs millions to run and GM will only allow approval for one base oil and additive combination. I found this on Chevron's PRO website... they make a lot of claims (all having to pass the sniff test from expensive lawyers)...