Explorers who purchased Glass already can upgrade to the new hardware version for free
Google announced today that it will be expanding the availability of Glass, as well as refreshing the hardware based on Explorer feedback. While there aren't any specifics on a new design or exact features, Google is saying that the new version of Glass will have compatibility with future prescription and sunglass lenses, and include a mono earbud. Presumably other hardware changes will be made as well — Google has been listening to those with Glass and tweaking the design accordingly.
Any of those initial Explorers with Glass who purchased a pair before today will be able to swap them out for the new version for free as well, which is a nice gesture to those who jumped on the $1500 bandwagon early. Furthermore, Explorers now have the ability to invite three friends to become Explorers and pay for their own pair of Glass.
The ability to invite friends will be rolling out in the next few weeks, and the big breakthrough here is that Google will simply let those new Explorers order Glass online and have it shipped to them. Previously, you had to make a trip to a Google office — more often than not involving an expensive flight and a hotel — to pick up a pair. Google isn't specifying how much these second-round Explorers will have to pay, but we're going to assume it's the same $1500.