RN at MS Office, Offline Apple AI, MCP at Home, RNEF×S3, Metro MF, New Testing Framework

Hey,

It’s Michał. Welcome to the May episode of our newsletter! Last month was rich with both experimentation and shipping new, sometimes long-awaited functionalities to projects in Callstack Incubator.

And speaking of shipping new stuff, we gave our website—and this newsletter—a fresh coat of paint. New look, same mission: helping you ship faster and scale with confidence using React & React Native, across every platform. How do you like it?

But back to the subject matter. We’ll talk about frameworks, microfrontends, new testing frameworks, and a bunch of news from the React and React Native communities. Let’s go!

Community highlights

• React Native runs in Microsoft Office: Chiara Mooney goes through how Microsoft uses React Native to implement Copilot—and 40 other experiences—across their Office suite, reaching over 600 million users.
• React Native Skia v2: macOS support, wide gamut colors by default on iOS, and bug fixes; requires React 19 and React Native 0.78. The team is also working on upgrading Skia to Graphite backend and WebGPU support, with 2-4x performance improvement potential.
• RN ExecuTorch 0.4.0: Another approach to running ML models and LLMs on-device; this release comes with tool calling, more LLMs available, text embeddings, multilingual speech-to-text and OCR, and image segmentation.
• React Native 0.80 RC: The next version is in the Release Candidate phase, coming with next-gen TypeScript API, support of radial gradient, React 19.1, redesigned community app template, warnings when the app runs in legacy architecture which is now frozen, and much more.
• React Router RSC: Preview support for React Server Components comes to React Router, integrating with loaders and actions, Server Component Routes, Server Functions (with "use server"), and client components (with "use client"). It will become stable as soon as RSC support lands in Vite.

Callstack Incubator highlights

React Native AI and MCP

The AI squad at Callstack Incubator was busy sharing knowledge on how the technology that powers on-device LLMs—MLC—works, how you can use MCP to control your friend’s home with Claude (if they let you), and how it compares to USB-C.

And right off the press, they’re cooking early support for the new Foundation Models API introduced at WWDC for iOS 26—as always, using the familiar AI SDK by Vercel.

Mobile microfrontends and Metro and Re.Pack

Last month, we introduced you to a pretty exciting project that Jakub, the maintainer of Re.Pack, has been recently working on: support for Module Federation in Metro. And he’s not slowing down, delivering more and more functionality, such as code-splitting for remotes (yes, not only in development) or shared dependencies, so that Metro MF can reach feature parity with Re.Pack at the end of June.

And while contributing to Metro, he also delivered Re.Pack 5.1 with a powerful runtime hooks system, persistent cache, preloading remotes, and more.

React Native Enterprise Framework

We promised and delivered: storing APK and IPA binaries on S3 is now generally available for all RNEF users. And since Cloudflare’s R2 is largely compatible with S3, we support that as well with the same API. We also released caching of local builds, so the next time you build the same project locally and change JS only, it will be pulled from the disk cache.

React Native Legal

We wrote a small piece on our blog about the react-native-legal project, which we announced a while back. What’s more exciting is that the project itself grows with new functionality and packages. Now, you can experimentally run the license-kit CLI to list licenses and check for usage of copyleft libraries in your code. It’s super easy to integrate with your CI actions, and we start to run these checks for every commit in some of our OSS projects.

New E2E testing framework

Szymon, our new team member, is working on something quite exciting (as a former Jest maintainer, I’m pretty biased here): a new end-to-end testing framework for React Native that allows you to run and preview your components in a real environment—no more mocking of native packages. You’ll be able to test your apps and libraries with this tool.

In addition to all of that, we released the following content pieces last month:

Blog

• Multithreading Isn’t Free: Performance Pitfalls Visualized by Mariusz Pasiński: This post demystifies multithreaded perf issues in C++ using Tracy. But even if you don’t write C++, the patterns and gotchas apply across the board.
• Meet react-native-ai: LLMs Running on Mobile, for Real by Szymon Rybczak & Kewin Wereszczyński: react-native-ai brings on-device AI to React Native apps. Built on MLC and the Vercel AI SDK, it offers a web-like dev experience—with native performance.
• New in Re.Pack 5.1 by Jakub Romańczyk & Szymon Rybczak: Module Federation preloading, runtime hooks, persistent caching, and more. This post covers everything new in Re.Pack 5.1, plus some major performance wins.

Podcast and videos

• React Universe On Air Coffee Talk #27 You Don’t Need a Rewrite, You Need React Native Brownfield: Burak Güner and Oskar Kwaśniewski explain how modern React Native Brownfield integration enables cross-platform power in native apps, without rewriting from scratch.
• React Native Optimization in Practice Episode 1: Auto Memoization with React Compiler: Ever wished you could skip writing all those React.memo() wrappers? In this episode, yours truly breaks down how React Compiler brings auto memoization to React Native—reducing re-renders and improving performance, without you having to lift a finger.
• React Native Optimization in Practice Episode 2: Why You Should Use Dedicated SDKs: In the second episode, we break down a common (and costly) mistake: using familiar web libraries in React Native apps. While generic-purpose JS libraries might be quick to integrate, they’re not built with mobile performance, UX, or reliability in mind.

Webinars and live streams

• Adding React Native to iOS and Android Apps Has Never Been Easier webinar: Learn how to easily add React Native to your iOS and Android apps with a modern brownfield setup powered by Callstack’s open-source tooling.
• From Hours to Minutes: Making Your React Native CI Builds 20x Faster webinar: Discover how to skip 90% of native builds in React Native CI using RNEF. Includes a live demo and cost-saving insights from Expensify’s setup.
• Master JavaScript Performance in React Native (Part 2) webinar: Learn to fix JS performance issues in React Native—from debounce bugs to Redux selectors—in this hands-on webinar with real code examples.
• Run LLMs Locally With React Native & MLC live stream: Watch how MLC brings on-device AI to React Native. See react-native-ai in action and discover what’s next for local model execution.
• What’s New in Re.Pack 5.1: Live Overview live stream: Explore runtime hooks, prefetching MF remotes, and more in Re.Pack 5.1.

Talks

• Building Universal Super Apps With React & React Native by Mike Grabowski: Discover how to build universal Super Apps using React and React Native. Join Mike Grabowski as he explores dynamic code delivery, native UI rendering, and how RePack bridges the gap with Module Federation.
• Bring Your Favorite Language to React Native by Robert Pasiński: Learn how to integrate native libraries in React Native, without TurboModules. Robert shares a practical approach using WebAssembly and introduces PolyGen.
• I Built a File-Based Router for React Native by Szymon Chmal: A deep dive into building a file-based router for React Native using Metro’s hidden APIs—dynamic routing, loading states, and smart hacks included.
• How to Make Your React (Native) App Feel Native by Oskar Kwaśniewski: How to make your React Native app feel truly native—across iOS, Android, tvOS & more. Dive into best practices, navigation, and react-native-bottom-tabs.

Where we’re heading

We’ve concluded a planning session for Q3 and, boy, we’re excited! Expect more AI tools that support developers, rethinking client-side observability, new approaches to test React Native libraries and apps (we mentioned it in Incubator Highlights), playing with navigation paradigms, and much more.

Upcoming events

• Mike at React Summit Amsterdam on June 13: our CTO takes the stage at React Summit Amsterdam to share insights on Building Cross-Platform Federated Modules with React, React Native, and Re.Pack. Come by if you're in town!
• React Universe Meetup: New York on June 24: We’re bringing React Universe Meetup to NYC! Expect talks on scaling full-stack mobile apps, modern brownfield integration, and observability at scale. RSVP here—we’d love to see you!
• Vercel Ship: After the NYC meetup, we’re heading straight to Vercel Ship. If you're attending, DM us—we're always up for a coffee or code chat.

React Universe Conf: 3 months to go!

We're full steam ahead prepping for React Universe Conf this September in Wrocław—and the lineup is already looking hot!

• New speakers: Zackary Chapple (Zephyr Cloud) and Adam Mruk (Klarna) will share hard-won lessons from scaling React Native in complex environments. Check their talks.
• Applications for Diversity & Volunteer programs close in June. Apply now if you haven’t yet!
• Workshops are coming soon—stay tuned for the full announcement.
• Special offer for you: Use code CK15 at checkout for 15% off tickets—exclusive to our newsletter readers. Valid through June only!

That’s it for May! Hope you found something useful, inspiring, or at least mildly entertaining.

Until next time—cheers!

Michał