The first 3.0 beta: one prop vocabulary across components, theme density, numbers on the spacing scale, merged components, and a codemod that migrates 2.x code.
Once UI 3.0 is the one breaking release we planned, and its first beta is on npm today. It gives every component the same prop names, adds a density setting to the theme, folds overlapping components together, and ships a codemod that moves your 2.x code over for you. 3.0.0 is planned for early January; until then the beta lives on the next tag.
npm i @once-ui-system/core@next
What 3.0 is
2.x grew one component at a time, and it showed. A toggle reported its state with onToggle, a field with onChange, a select with onSelect. A colour role was variant on a Button, scheme on a Tag and state on a Timeline. A bare number meant rem on a width and a percentage on a mask. 3.0 settles each of these once, so what you learn on one component holds on the next. It is a cleanup, not a redesign: apps look the same after the move.
How to try it
Start on a 2.x app with a clean working tree, and upgrade react and react-dom to 19 first, since React 19 is now the floor. Then run the codemod while the app is still on 2.x. It is a script in the core repo, not a package, so clone the beta tag next to your app and point it at your source:
git clone --depth 1 --branch v3.0.0-beta.0 https://github.com/once-ui-system/core ../once-ui-core
node ../once-ui-core/scripts/codemod-3.0.mjs src --dry # see what it would change
node ../once-ui-core/scripts/codemod-3.0.mjs src
npm i @once-ui-system/core@next
It only touches Once UI's own components, and running it twice changes nothing. Lines marked ! in its report are the spots it could not rewrite exactly, each with its file and line, for you to finish by hand. The migration guide walks through every step.
One thing to hold back for now: the effects (RevealFx and the other Fx components) and blocks such as StylePanel and Banner move to their own packages in 3.0, and those are not on npm yet. If your app uses them, wait until those packages are published before you migrate it.
The 3.0 docs are live on their own site while the beta runs:
