Our fitness kit's iOS build used to take 14 minutes on CI. After upgrading to Expo SDK 54, it takes 4. That's not a CI optimisation. We didn't add parallel runners or bump the machine size. We just landed on the SDK that ships precompiled XCFrameworks by default. Same code, same build profile, same EAS plan — 70% time reduction. Worth understanding what Expo actually changed. What got precompiled Historically, every iOS Expo build had to compile the entire React Native core and all native module