Vaadin will keep using web components for reusable components. Those components are historically built using Polymer but there’s an initiative ongoing to migrate them to use Lit instead. For building applications, we support both server-side Java through Flow and client-side TypeScript through Hilla.
With Flow, the server-side component APIs remain as the main recommended way of defining the component tree and the UI logic. There’s also the possibility of using the LitTemplate Java class to define the component tree using Lit. We’re also considering a similar option based on JSX and React.
For Hilla, we will recommend using React but will keep supporting Lit as well. See this post for more details about Hilla.