Expo SDK 55 Beta: The Big Changes You Need to Know

Expo SDK 55 beta dropped last week, and this one's significant. If you're building React Native apps with Expo, here's what you need to know before upgrading.

Legacy Architecture is Gone

This is the big one. SDK 55 completely drops support for the Legacy Architecture. The newArchEnabled config option? Gone. If your app still relies on legacy-only libraries, you'll need to update them or find alternatives before upgrading.

The New Architecture has been stable for a while now, so this isn't surprising - but it's worth checking your dependencies.

Hermes v1 (Opt-In)

The new Hermes engine brings real performance improvements and better support for modern JavaScript - proper ES6 classes, const/let, async/await. You can try it now:

{
  "expo": {
    "plugins": [
      [
        "expo-build-properties",
        {
          "buildReactNativeFromSource": true,
          "useHermesV1": true
        }
      ]
    ]
  }
}

Fair warning: this requires building React Native from source, which adds significant build time. Test it, see if the performance gains are worth it for your app.

75% Smaller OTA Updates

This one's exciting. Hermes bytecode diffing is now available for expo-updates and EAS Update. Instead of downloading the entire JS bundle for each update, your app downloads just the binary diff.

The result? Approximately 75% reduction in download sizes. Faster updates, less bandwidth, happier users.

{
  "expo": {
    "updates": {
      "url": "https://u.expo.dev/<id>",
      "enableBsdiffPatchSupport": true
    }
  }
}

It's opt-in for SDK 55, will be default in SDK 56.

New Project Template

The default template got a redesign:

• Native Tabs API for platform-native tab navigation
• New /src folder structure - your app code lives in /src/app instead of /app
• Better separation of code from config files
• Refreshed design out of the box

AI Tooling for Devs

Expo's leaning into AI-assisted development. The MCP server now supports CLI actions, and there's an official expo/skills repo with agent skills for Claude Code and other AI tools. If you're using AI coding assistants, these are worth checking out.

Should You Upgrade Now?

The beta period runs about two weeks. If you have time to test, jump in - the Expo team is actively fixing issues during beta, and your feedback helps. Join their Discord office hours if you hit problems.

For production apps, wait for stable unless you're comfortable debugging regressions. But definitely start planning your migration, especially if you need to audit dependencies for New Architecture compatibility.

The upgrade guide will drop with the stable release. Until then, check the changelog for breaking changes.