I believe they are all hollow - it'd be super-heavy if they aren't. Vid of manufacturing process:
From the sound of it they are basically creating units using glass brick as a cladding material (backed up by reflective sheeting and probably insulation). The catch is they won't be visually translucent (to the interior of the building) - maybe there are sections where it won't get this treatment?
There's a mix of opaque and translucent blocks. From a UT story:
"The materials include glass block with a mirrored back coating for walls that are opaque on the interior, creating depth and radiance when the sunlight hits them. In other places, the glass block will be translucent on both sides, allowing daylight in for residents or providing a glow on the exterior at nighttime."