When it’s released, React 18 will include out-of-the-box improvements (like automatic batching), new APIs (like startTransition), and a new streaming server renderer with built-in support for React.lazy.

These features are possible thanks to a new opt-in mechanism we’re adding in React 18. It’s called “concurrent rendering” and it lets React prepare multiple versions of the UI at the same time. This change is mostly behind-the-scenes, but it unlocks new possibilities to improve both real and perceived performance of your app.

If you’ve been following our research into the future of React (we don’t expect you to!), you might have heard of something called “concurrent mode” or that it might break your app. In response to this feedback from the community, we’ve redesigned the upgrade strategy for gradual adoption. Instead of an all-or-nothing “mode”, concurrent rendering will only be enabled for updates triggered by one of the new features. In practice, this means you will be able to adopt React 18 without rewrites and try the new features at your own pace.

 

A gradual adoption strategy

Since concurrency in React 18 is opt-in, there are no significant out-of-the-box breaking changes to component behavior. You can upgrade to React 18 with minimal or no changes to your application code, with a level of effort comparable to a typical major React release. Based on our experience converting several apps to React 18, we expect that many users will be able to upgrade within a single afternoon.

 

We successfully shipped concurrent features to tens of thousands of components at Facebook, and in our experience, we’ve found that most React components “just work” without additional changes. We’re committed to making sure this is a smooth upgrade for the entire community, so today we’re announcing the React 18 Working Group.

Accessing the React 18 Working Group

Everyone can read the discussions in the React 18 Working Group repo.

Because we expect an initial surge of interest in the Working Group, only invited members will be allowed to create or comment on threads. However, the threads are fully visible to the public, so everyone has access to the same information. We believe this is a good compromise between creating a productive environment for working group members, while maintaining transparency with the wider community.

As always, you can submit bug reports, questions, and general feedback to our issue tracker.