There's a bunch of extra function keys that extend the modern standard of CTRL-ALT-DELETE and supposedly enabled 8k command combinations that were useful for lisp machines. However, the later versions of them didn't have the same color scheme and dropped many of the additional keys for simplicity.
there will probably be another edition eventually but as someone still somewhat noobish to this hobby i've heard lots of people are ok waiting a year or two for a new group buy to start for a specific set. If you want one now keep searching /r/mechmarket for "space cadet" and make sure you look into the different kinds of sets. Mine was $170 with shipping from europe, but there are less keys on my ergodox keyboard and the set was made specifically for them. A full set is probably somewhere between $200-300. I think I've seen them for the low end of that but I'm not sure. If you don't have to have something identical, there's an SA profile set for $100 that's just blue/gray without the special characters you see in the photos. You'd have to do some googling to make sure the sa profile fits on your keyboard though. Usually they will but sometimes people have issues so I'd research:
This is a chinese site, but very reputable. There are other places that stock the same set:
https://imgur.com/r/mechanicalkeyboards/BjycwBN
Here's the link to the keycaps alone with better pics. Unfortunately only available aftermarket now.
https://drop.com/buy/massdrop-x-oblotzky-gmk-space-cadet-key...
And here's the original:
https://www.rcsri.org/collection/symbolics-keyboards/symboli...
There's a bunch of extra function keys that extend the modern standard of CTRL-ALT-DELETE and supposedly enabled 8k command combinations that were useful for lisp machines. However, the later versions of them didn't have the same color scheme and dropped many of the additional keys for simplicity.