While a non-AR ARView is on screen and rendering, await Entity(contentsOf:) takes about 26 s to load a 4.5 MB USDZ with 300 textured meshes. The same file loads in about 1.5 s with the synchronous Entity.load(contentsOf:), or with the async API while the view is hidden. iPhone 16 Pro, iOS 27.2Mac Catalyst, macOS 27.2await Entity(contentsOf:), view rendering22 to 26 s26 sEntity.load(contentsOf:), view rendering1.6 s1.1 to 1.7 sawait Entity(contentsOf:), view hidden1.4 s1.3 to 1.5 sModelEntity(contentsOf:) and Entity.loadAsync(contentsOf:) behave the same. A .reality file loads fast either way, and the iOS Simulator doesn't show it. A Time Profiler trace shows the main thread blocked in re::RenderThread::waitForFramePacing on every frame, so the @MainActor import only advances between frames. Neither workaround fits loading content into a scene the user is looking at: the sync load blocks the main thread, and hiding the view blanks it. Filed as FB25340264, with a sample project.

Async Entity(contentsOf:) is 15 to 20x slower while an ARView is rendering

While a non-AR ARView is on screen and rendering, await Entity(contentsOf:) takes about 26 s to load a 4.5 MB USDZ with 300 textured meshes. The same file loads in about 1.5 s with the synchronous Entity.load(contentsOf:), or with the async API while the view is hidden.

iPhone 16 Pro, iOS 27.2Mac Catalyst, macOS 27.2

`await Entity(contentsOf:)`, view rendering	22 to 26 s	26 s
`Entity.load(contentsOf:)`, view rendering	1.6 s	1.1 to 1.7 s
`await Entity(contentsOf:)`, view hidden	1.4 s	1.3 to 1.5 s

ModelEntity(contentsOf:) and Entity.loadAsync(contentsOf:) behave the same. A .reality file loads fast either way, and the iOS Simulator doesn't show it.

A Time Profiler trace shows the main thread blocked in re::RenderThread::waitForFramePacing on every frame, so the @MainActor import only advances between frames.

Neither workaround fits loading content into a scene the user is looking at: the sync load blocks the main thread, and hiding the view blanks it.

Filed as FB25340264, with a sample project.