Svelte tries to improve upon the relatively complex/heavyweight runtime of something like React by shifting as much of that complexity to the build step as possible. It also takes a more "batteries-included" approach compared to React by including some opinionated features like state management, animation, transitions and the like.

I haven't dug too deeply into Svelte because last I checked it didn't play particularly nicely with TypeScript but this release may prompt me to give it another look.