The last CPU that was being developed at Symbolics is actually RISC: https://en.wikipedia.org/wiki/Symbolics#Sunstone

The competitor LMI was also developing their next-generation Lisp machine RISC processor: https://en.wikipedia.org/wiki/Lisp_Machines#GigaMos_Systems

More about the latter: http://fare.tunes.org/tmp/emergent/kmachine.htm

Well, Symbolics did not manufacture the new CPU. That would have been too costly.

LMI manufactured prototypes of their CPU, but these were older technology - not microprocessors, but VME-board sized CPUs.

Xerox mantioned that they were developing a Lisp RISC, but it never surfaced. The SPUR project designed a Lisp RISC Chip: ftp://ftp.cs.wisc.edu/markhill/Papers/jsscc89_vlsi_spur.pdf

? x86 is obviously very CISCy. Another example is IBM's Z architecture which they keep making faster and faster. The argument is _economical_ not technical.

IOW, the architectural benefit for Lisp machine weren't enough to overcome the benefit offered by Moores law. Today, things look different but it would be a much harder sell to push Lisp or any non-C launguage.