Actually, the new SSI standards include distinctions between Dive Guide (DG), Dive Master (DM) and Dive Con (Dive Control Specialist/Certified Assistant Instructor)
The Dive Master prerequisites are: 18 years old, certified as a Dive Guide or equivalent, 50 open water dives totaling 32 hours or more.
Certification requirements are: Completed Dive Guide certification and Science of Diving Specialty program, First Aid/CPR/O2, Insurance, 60 Open Water Dives totaling 40 hours or more.
Dive Con has similar requirements with additional academic and pool sessions, 75 open water dives, totaling 50 hours or more.
Dive Guide requires AOW + Stress Rescue, so pretty much the same requirements as the old Dive Con standards, but now there are distinct standards for Dive Guide, Dive Master, and Dive Con. Dive Guides/Dive Master may not teach Scuba Skills Updates, or teach any portion of the Open Water class (under direct or indirect supervision).