This demo animates the ticker with requestAnimationFrame mutating transform frame by frame, so Chrome does not composite it on its own. Open the demo in a tab, enable Paint flashing in the Rendering panel and watch the Layers tab: with the toggle off you'll see the #document repainting; turn it on and will-change gives it its own layer, and the repainting stops. To see it already fixed from the first render (without the initial non-promoted state), open the demo with ?promoted in the URL. The Repaints counter in this demo updates live so you can see the difference; in the real Layers panel, however, the Paint count is a snapshot that only changes when you reselect the layer, so use Paint flashing as the real-time signal.