Concurrent Mode is an advanced feature in React that allows the library to work on multiple tasks at the same time.
Instead of blocking the user interface while performing heavy updates, React can pause, abort, restart, or prioritize different updates to keep the app feeling fast and responsive.

It’s not a new rendering engine — it's a set of new capabilities that improve React apps’ ability to handle complex updates without freezing or becoming unresponsive.

In short:

Concurrent Mode makes React apps more responsive by rendering work in a more interruptible and prioritized way.

React enables Concurrent Mode selectively; you choose which parts of your app opt into it, allowing a smooth upgrade path.

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