UI Toolkit is built into Unity as a core part of the Editor. It is also available as a package, called com.unity.ui, which is currently in preview. The built-in version for each major Unity release is based on a specific version of the package, but the two are not completely identical.
The built-in version of UI Toolkit includes the features required to make user interfaces for the Unity Editor. The package version contains the exact same features, as well as the features required to make runtime user interfaces for games and applications.
Both versions of UI Toolkit work exactly the same way, and use the same namespaces:
UnityEngine.UIElements. If you install the package, you will not see any difference other than having access to the additional runtime features. You do not need to do any additional configuration.
Whether you use the built-in version of UI Toolkit or the package depends on what type of user interfaces you plan to make.
You may also want to install the package if you want early access to the very latest UI Toolkit features. Unity may release preview versions of the com.unity.ui package between major Unity releases.
|Preview versions of com.unity.ui might contain features that are not stable or final. Avoid using preview versions in production.|
You install the UI Toolkit package from the package manager:
The package manager automatically finds and installs the UI Toolkit package.