So far, the hardtop is a racing only hardtop.... for Solstice only
The top lacks weather seals, and doesn't allow the trunk to be opened.
It's not designed for regular highway use, the top that GM is selling is a purpose built racing top that meets the requirements for SCCA Showroom Stock B category safety requirements.
To get one, you can order one, but you must be a currently licensed SCCA driver, and they require your SCCA license number to sell it to you. (This is being done so that the tops do wind up in the hands of racers who will use the for racing)
Also, keep in mind to, that the profile of the mating surfaces for the top may be slightly different for the Solstice than for the Sky, and while it might be possible to get the top to fit on the Sky with it's more angular aero head fairings, I am willing to bet some modification of the top would be necessary.
The link posted above by 1994SC2 to the Solstice forum has a great deal more detail about this purpose built Carbon Fiber racing only top.
Here's that link again courtesy of 1994SC2:
Solstice Hardtop Z0K? [SSB Z0K Racing Solstice Pics]