SvelteKit 3 moves configuration from svelte.config.js to vite.config.ts so the Vite plugin can read config synchronously. The $lib alias is replaced by lib subpath imports per standard JavaScript conventions.
SvelteKit 3 requires Vite 8 and its Rolldown bundler for faster builds. Remote functions — a type-safe client-server RPC approach — remain behind an experimental Async Svelte flag.
The stable 3.0 release shipped October 1, 2026 with an sv migrate command for automated codebase upgrades.