Introduction

If you haven’t upgraded to React Native 0.84 yet, you’re literally leaving free performance on the table.

In early 2026, the React Native team released version 0.84 and has made Hermes V1 the default JavaScript engine for both iOS and Android. No config changes required. No migration steps. Just npx react-native upgrade (or create a new project) and you instantly get:

• Faster JavaScript execution
• Lower memory footprint
• Smoother 60 fps animations & lists
• Faster cold starts

This is the single biggest “set it and forget it” improvement React Native has shipped since the New Architecture became default in 0.82.

In this post we’ll look at why Hermes V1 matters so much in 2026, how to verify it’s active in your app, a real-world code example that shows the performance difference clearly, and what to expect when measuring it.

1. What changed in React Native 0.84?

Hermes has been the default engine since 0.70, but Hermes V1 (released in stages during 2025 and stabilized in 0.84) brings a rewritten compiler, new bytecode format, improved JIT, concurrent garbage collection (Hades), and better handling of modern JavaScript patterns used by React 19+.

Real-world numbers reported by teams after upgrading to 0.84 (Hermes V1 default):

• 25–55% faster JS execution in heavy components
• 15–40% lower memory footprint
• 10–30% faster cold start time (especially noticeable on low-end Android devices)
• Significantly reduced jank/lag during typing + filtering + sorting operations

And again: no code changes required.

2. How to confirm Hermes V1 is running

Drop this snippet anywhere in your app (e.g. in useEffect in App.js):

Checking Hermes

Typical Output on 0.84+ —-

Hermes active — OSS Release Version: 250829098.0.9
Likely Hermes V1? YES

3. Practical example: Heavy Searchable List

This component simulates a real e-commerce / analytics screen: 5,000 items, live filtering + sorting + calculations on every keystroke.

Heavy Computation

Typical timings observed in 2026 (RN 0.84, Hermes V1 default):

Debug: 2–15 ms per keystroke (very smooth)
Release: often 1–8 ms
Older Hermes or JSC: frequently 50–250 ms → visible typing lag

Search Execution Time

4. Measuring with the new React Native DevTools

Open DevTools (bundled since 0.84), go to Performance tab, record while typing and scrolling. You’ll see dramatically shorter JS execution bars compared to older versions.

JS Execution Bars

Conclusion

React Native 0.84 with Hermes V1 default is one of those rare upgrades where you literally get better performance for free — no migration pain, no new architecture headaches, no rewriting business logic.

If your app involves any kind of dynamic lists, search-as-you-type, real-time calculations, or complex component trees, upgrading to 0.84 will almost certainly feel noticeably snappier — especially on mid-range Android devices.

New project? → just use latest (npx react-native@latest init)
Existing app? → run npx react-native upgrade and measure

Hermes V1 isn’t flashy marketing — it’s quiet, boring, excellent engineering that makes every user interaction a little faster.

Thank You