Yes, but to my knowledge anyone could in principle build CLOS in a LISP that didn't have it. It is basically a selection of macros and functions. It did not require any significant changes to the LISP language itself as far as I know.

It is one of the powers of LISP that they could experiment with different object systems easily without languages changes until they landed on CLOS.

It is a bit different from say Julia, which has a CLOS like system which is very much a part of the language. You cannot define a function in Julia which doesn't have methods and doesn't use multiple dispatch.