React 19 upgrade reverted; plugin compat issues found

Few days ago we announced that WordPress and Gutenberg are upgrading to React 19. But soon after publishing a Gutenberg version with the upgrade (23.3.0) we discovered that many plugins that were built for the previous version of WordPress, with React 18, are incompatible with the new version and crash often.

While there are virtually no API changes between React 18 and 19, the runtimes turned out to be incompatible in unexpected ways. For example, many plugins bundle their own version of the react/jsx-runtime helper used to process JSX syntax, but the shape of the generated objects (elements) is different, and React 19 actively checks and rejects elements generated by the React 18 runtime.

We’ll have to devise a better, less naive and more incremental upgrade strategy. With ability to switch between React 18 and 19 with an experimental feature flag, and with a compat layer for already released plugins. In the meantime, we decided to revert back to React 18, and released the revert in Gutenberg 23.3.2. This gives us time and breathing room to think the new strategy through and test it thorougly. We continue to be committed to doing the upgrade in WordPress 7.1.