It is of course a Lisp "Space Cadet keyboard" but specifically this one went with a Lisp CADR machine. The CADR machine was actually the second machine designed at MIT with the first one called CONS. Apparently there were maybe a total of 25 of these essentially prototype machines which were sold and used extensively by MIT. Later when the Symbolics Corporation was formed they cleaned up the CADR design and sold it as the LM-2 which is were we see the first Symbolics branded "Space Cadet" branded keyboards with the beige case.
Per Wikipedia: "Symbolics did get off the ground in 1980/1981, selling the CADR as the LM-2, while Lisp Machines, Inc. sold it as the LMI-CADR" so based on the brochure I found this keyboard was from the LMI-CADR so not a prototype but still exceedingly rare.
OG - The first of the Lisp Machine keyboards, called the Knight keyboard after Tom Knight, who did design work on the whole thing.
http://graflex.org/klotz/2003/aitv/ SAIL (Stanford AI Lab) version:
Symbolics LM-2 model 1st Gen (1981):
https://www.youtube.com/watch?v=oDozftThFMw - Chryos you should do an update or a part 2 now
http://rcsri.org/collection/symbolics-keyboards/ Symbolics 36xx series 2nd Gen (1983): LMI Lambda Machine 2nd Gen (1983)
https://www.reddit.com/r/MechanicalKeyb ... s_popular/ Webwit's Lisp boards:
https://www.reddit.com/r/MechanicalKeyb ... 89el/lisp/
Limited backstory, the seller had two LMI-CADR Lisp machines which were sold ages ago. While going through storage were two of these keyboards which were spares. Both of which sold on eBay today and I bought the second.