What is this new shipping size OS1 and OS2 that UPS has initiated?

ANSWER:

OS1 and OS2 are size to weight measurement used to determine the shipping costs for larger packages via UPS ground shipments.

A package that meets the OS1 size will ship at actual weight or 30 lbs whichever is higher.

A package that meets the OS2 size will ship at actual weight or 70 lbs whichever is higher.

It is to your advantage to pack carefully.  Cutting a box down to size to meet below OS1 or OS2 size can save you a lot of money.  HOWEVER.... Don't risk improper packing methods.  Irregardless of cost, it is better to pay the higher cost, then to have a package arrive damaged.  More importantly it is better to use proper packing techniques then to have a UPS claim denied for improper packing.