Core Animation is designed to move work related to playing animations off of the app's main thread. Animations are instead performed by a different process, the

Core Animation is designed to move work related to playing animations off of the app's main thread. Animations are instead performed by a different process, the OS render server. The UIViews / CALayers / CAAnimations themselves have to be configured on the main thread, but the work to actually play the animation and render each individual frame doesn't happen on the main thread.