The first paragraph of the press release says it all - the lightest weight in its class and it's a 100-400mm zoom!
The advanced optical design of Model A035 includes 3 LD (Low Dispersion) lens elements for greater aberration reduction and Tamron's original eBAND Coating for superior anti-reflection performance. At 39.3 oz., the new lens is the lightest weight in its class and features magnesium material in key areas of the lens barrel to improve weight reduction, strength and portability.
The press release will take you through the highlights of this new member of the Tamron family. As I've written before, Tamron isn't just building great optics, they're helping artists capture greater images!