The View Transitions API lets the browser animate between two DOM states. Wrap a DOM mutation in document.startViewTransition(callback) and Chrome will snapshot the before and after, then cross-fade them.
It is well-supported in Chromium and shipping in Safari 18 with the cross-document variant landing across 2025. The same-document variant works today on Chrome and is a progressive enhancement everywhere else.
The killer use case is single-page navigation in MPAs — every link feels instant without committing to a JavaScript router.