By Expo SDK 55 shipped in February 2026 with React Native 0.83 and one change that carries no asterisk: the Legacy Architecture is gone. Not deprecated, not behind a flag — removed. If your production app still has newArchEnabled: false in its app.json, that line is silently ignored. Your app is running on the New Architecture whether you planned for it or not. And if you haven’t upgraded past SDK 54 yet, you’re sitting on a branch that receives no security patches, no bug fixes, and no React Native updates beyond 0.81. This is your migration guide.
Who This Affects
If you’re already on SDK 54 with the New Architecture enabled, this post is mostly good news — you can upgrade cleanly. If you’re on SDK 53 or earlier, you’re facing a multi-version jump and need to go one step at a time: 53 to 54 first, then 54 to 55. And if you’re among the roughly 17% of EAS Build projects that hadn’t migrated to the New Architecture as of January 2026, this is the moment to stop deferring.
The legacy architecture was frozen in June 2025. That means it received no new features and no security patches from that point forward. Running it in production today means running on an unpatched code path.
Why the New Architecture Is Worth the Work
The performance numbers are real. The New Architecture eliminates the JSON serialization bottleneck that defined the old Bridge — native calls drop from roughly 200ms to 2ms per call. TurboModules load native dependencies lazily rather than eagerly at startup, translating to 80% faster native interactions. Production migrations from teams that have made the jump report 43% faster cold starts, 39% faster rendering, and 26% lower memory usage.
Beyond raw performance, the New Architecture enables React 19’s concurrent features — useTransition, useDeferredValue, and Suspense integration — to work as designed. It also enables synchronous layout measurement, which is what makes advanced Reanimated and gesture handler patterns actually reliable instead of occasionally wrong.
The Migration Steps
The official upgrade process is four commands and one file edit:
# Step 1: Upgrade Expo and fix dependencies
npx expo install expo@^55.0.0 --fix
# Step 2: Remove newArchEnabled from app.json (delete the line entirely)
# "newArchEnabled": false ← this line should not exist
# Step 3: Validate your dependencies
npx expo-doctor
# Step 4: Regenerate native code
npx expo prebuild --clean
# Step 5: Test on both platforms
npx expo run:ios
npx expo run:androidStep 3 is the one most developers skip and later regret. expo-doctor integrates with the React Native Directory to flag every library in your project that is incompatible or untested with the New Architecture. Run it before touching anything else. It tells you where your problems are going to be before you build.
Handling Incompatible Libraries
The interop layer — available since React Native 0.74 — means most older libraries continue to work on the New Architecture without any changes. The Expo team has committed to keeping the interop layer in React Native for the foreseeable future, so this isn’t a temporary crutch. Libraries most likely to have issues are those that ship heavy native code or depend on third-party native SDKs directly.
When expo-doctor flags a library, your options in order of preference: check for an updated version, use the interop layer (usually automatic), or find a New Architecture-compatible replacement. For most common dependencies, someone has already solved this and the solution is a version bump.
If you’re jumping from SDK 53 to 55, upgrade incrementally. The jump spans two React Native major versions (0.79 to 0.83) and a Reanimated v3-to-v4 migration on top of the architecture change. Going 53 to 54 first isolates issues to one version step, making failures much easier to diagnose.
What Else Landed in SDK 55
The architecture removal is the headline, but SDK 55 ships several other meaningful changes worth noting as you plan your upgrade:
- Hermes bytecode diffing: OTA updates via EAS Update are up to 75% smaller. The client now applies binary patches to previously installed bytecode instead of downloading complete files. This is opt-in in SDK 55 and becomes the default in SDK 56.
- Expo Router v7: Adds a Zoom transition, Stack.Toolbar API, and dynamic color support. If your app uses Expo Router, review the v7 migration notes — some APIs changed.
- expo-widgets: Create iOS Home Screen Widgets and Live Activities using Expo UI components without writing native Swift or Objective-C.
- expo-brownfield: A new isolated brownfield approach that packages your React Native code as a native library (AAR for Android, XCFramework for iOS), letting native teams consume it without setting up Node.js or the React Native build toolchain.
- AI tooling: MCP server integration with Expo CLI and EAS, plus official agent skills for AI-assisted development workflows.
After the Upgrade
One step developers frequently miss: create a new development build after upgrading. Expo Go is not the recommended development environment for production apps, and an SDK 55 project needs an SDK 55 development build to test accurately. Run eas build --profile development or npx expo run:ios to generate a fresh build.
Check your version now. SDK 54 is still receiving maintenance, but that window will close. The 83% of EAS Build projects that already migrated did so before the removal — the tooling is mature and the interop layer handles the long tail. For the remaining 17%, the process is not painless, but it is well-documented and the end state is a faster, more capable app running on supported infrastructure.
The full SDK 55 changelog, the official upgrade guide, and the New Architecture documentation cover every edge case. Run expo-doctor first. That’s the rule.
