>Coalton strives to implement Haskell or ML-adjacent semantics (in the type system, for example) with Lisp syntax. "With" here meaning that it is both implemented in and written with Lisp syntax.

Not exactly. Coalton brings ML-style strong typing to Common Lisp. But Coalton code is also Lisp code.

The backend, thus, is Common Lisp, and it is available at all times, thus leveraging all its power.