From https://github.com/flutter/engine/wiki (more there about the Flutter engine):

Flutter has several threads; the shell code runs on the system’s “main UI thread”, the Dart library runs the Dart application code in a second thread, and Skia runs on a third thread (the “GPU” thread, because it talks to the GPU). We also execute I/O and image decoding on separate threads.

It is very unlikely the problem in the original comment is architectural. The animations in the Flutter Gallery are definitely not slow. We’ve seen bugs in some older phone’s GPUs in the past that can cause slowdowns. We appreciate everyone’s help in tracking them down!