Upload & Sell: Off
I didn't expect them to turn this into a GM. I thought it would be a G. Then again who cares about naming . Seems Sony squarely aimed at Canon 100-400 L II. As we know, the Canon lens is extremely good. If they managed to produce a lens that performs as well or slightly better, this should be a great long zoom.
Personally, I'm more interested to see how this compares to the a-mount 70-400G2, because I have plenty of experience with that zoom. The a-mount lens is slightly shorter, but 100g heavier. The GM also has larger magnification (0.35x versus 0.27x). Given the inclusion of OSS and the more complex design (22 versus 18 lens elements), I think they moved the wide end up to 100mm (from the traditional 70/80mm) to keep things reasonably compact.
Fred: I think the first post needs updating, whenever you get to it. The above specs are quoted from B&H's website. The weight, size (at least in cm) and the filter thread size all seem off (assuming the B&H specs are correct. My guess is they are, seeing how they are close to the 70-400G2).