One of the defining characteristics of the Escala were narrow, horizontal headlights, while the current CT6 has long, vertical lamps that go up the tops of the fenders. This prototype seems to split the difference. The bases of the lights terminate higher up on the fascia, emulating the Escala, but still travel up the fenders. It also appears that the LED accent lights remain, but it's possible they've been separated from the main lamps to become more like the concept.
The grille has also been revised. It's hard to make out the exact shape, but the insert is the same type of mesh as the Escala's, with little highlights that look like miniature Cadillac crests. The full-size, full-color crest also appears to sit higher in the grille, which is another nod toward the concept. The lower grille in the front bumper also looks larger and more angular. That doesn't really lean toward either model, but should give the car an edgier look.
The rest of the car looks generally the same as the current model. Even the tail shows little indication of changes. It's possible that the rear taillights could have an Escala-like horizontal section at the top of the trunk lid, but there's nothing visible on this prototype that would confirm that change either way. Since this is a relatively mild refresh, we would expect to see it fully revealed early next year.