I wanted to give everyone a heads up regarding running Cesium on iOS 9 and OS X El Capitan (Safari 9), both of which are being released later this month.
Unfortunately, Apple has introduced a bug that breaks Cesium on all iOS 9 devices and under Safari 9 on the desktop. While they are aware of the bug, it will not be fixed in time for release. We have already introduced a workaround in Cesium master (see #3024), but all existing versions of Cesium will remain broken on Apple browsers until they address the issue. This means that if you want your Cesium-based application to run on iOS 9 (all browsers) or Safari 9 on OS X, you will need to update to the latest version of Cesium when it is released on October 1st.
Once Apple fixes the issue, old versions of Cesium should work again, but I’m sure most people would rather not wait.