Internals: How Flutter 4.0's Impeller Engine Renders Faster Than React Native 0.75 on iOS 18

Apple’s iOS 18 update brought new Metal 3 API enhancements and tighter GPU scheduling constraints, making cross-platform rendering performance more critical than ever. This deep dive compares the rendering internals of Flutter 4.0’s Impeller engine and React Native 0.75’s Fabric renderer to explain why Impeller delivers consistently faster frame rates on iOS 18 devices.

Background: Rendering Pipelines 101

Both frameworks aim to deliver 60/120fps smooth UIs, but their approaches to bridging JavaScript/ Dart code to native iOS GPUs differ fundamentally. React Native 0.75 uses the Fabric renderer, which relies on a bridge to pass UI commands from JS to native Objective-C/ Swift views, then composites them via UIKit’s Core Animation.…