SvelteKit 3 is frozen ahead of a stable release, so run the sv@next migrate sveltekit-3 path now and handle the breaking changes on your own timeline.
SvelteKit 3 hit release candidate on August 13, and the team promises no further breaking changes before stable lands "in the near future." That is the whole pitch: the API you test now is the API you ship on. Run the migration on your own schedule instead of learning a breaking change exists on release day.
The path is sv@next migrate sveltekit-3. The change with the most surface area is $lib becoming #lib, a switch to Node subpath imports that rewrites imports throughout your app. Config moves from svelte.config.js to vite.config.ts, so your Svelte and Vite settings finally live in one file. TypeScript setup shrinks too: you extend $app/tsconfig instead of hand-maintaining your own compiler options.
Runtime behavior changes more than file layout. Error boundaries now require Svelte 5, and all errors route through handleError, which gives you a single funnel for reporting. The service worker API got a facelift, and env var handling changed, so both deserve a look during review.
Run sv@next migrate sveltekit-3 in a branch now, diff every changed line, and sort out the surprises before stable drops. The tool does the mechanical work. The judgment calls are yours.
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