We can't just call it the Jam anymore, they're all the Jam, just in three different (35, 50, 70 liter) sizes.
Stock weight of the large 50L is 31 oz (I got this wrong in that other thread). In many/most respects, it's the same as the 2011. Size looks the same, compression system is the same, big rear pocket is similar, etc. Bladder sleeve is now lighter stretch mesh and huge, the size of the whole inside back panel. Side pockets are the same stretch mesh, and seem a bit taller and stretchier than the 2011 ones. Reachable with the pack on, but only just. A few details save a bit of weight over the 2011, for instance the inside of the big pocket is a light ripstop, not the heavier Gridstop. It has load lifters, and softer foam in the shoulder straps. I worry about that, as I really liked the 2011 Jam straps. Center stripe of heavy-guage 3D mesh on the back is the same. Adds weight, but actually allows air circulation, increases traction of the pack and thus improves load carry, and provides some resistance against rubbing the tailbone and vertebrae. Foam framesheet appears to be identical to the 2011.
The biggest difference is the hipbelt. Much wider and longer than the previous version, with similar foam to the straps, which seems resilient but is quite a bit more flexible than the 2011 foam. The pockets are huge, with the lower part being the same stretch mesh as the side pockets, and the gussets being substantial. They'll hold lots, even with the pack on.
I predict a lot of folks are going to like this belt a lot. But some folks, namely those much skinnier than me (32" jeans) with long torsos, are not going to be able to use this pack. As you can see, I have about 1.5" of slack left in the belt. I do tend to where by belt higher than many, however.
Time will tell. In any case, Golite is not resting on their laurels, and easy though it may be to snipe about GoHeavy, the jam remains a solid option. It unites value, durability, and a sensible and versatile feature set in a way which no other commercially available pack does.