Why the key was renamed
Rolldown, not Rollup, is Vite 8’s production bundler. Vite’s migration guide lists the rename directly under “Deprecated Options”: build.rollupOptions → build.rolldownOptions, alongside the same rename for worker.rollupOptions → worker.rolldownOptions.
build.rollupOptions is one of the single most commonly customized Vite options. It’s where manualChunks, external, and custom output naming patterns live for most real projects. That popularity is exactly why this deprecation is loud: any project with a nontrivial build config sees the warning on every single build the moment it upgrades to Vite 8, even though nothing is actually broken yet.
Fix it: rename the key
Before: the deprecated key
export default defineConfig({
build: {
rollupOptions: {
output: {
manualChunks(id) {
if (id.includes("node_modules")) return "vendor";
},
},
},
},
});After: the same config under the new key
export default defineConfig({
build: {
rolldownOptions: {
output: {
manualChunks(id) {
if (id.includes("node_modules")) return "vendor";
},
},
},
},
});Nothing inside the object changes. If your project also customizes worker.rollupOptions for a web worker build, rename that key the same way.
Check manualChunks while you're in there
If your manualChunks uses the older object-map shorthand instead of a
function, the rename alone won’t fix your build. Rolldown only supports the
function form. See Fix Vite 8 manualChunks Object Form
Removed for that
separate, sharper break.
Confirmed version range
Documented in Vite’s own current migration guide as an intentional Vite 8 rename, auto-mapped for backward compatibility today. This site’s own astro.config.mjs doesn’t customize build.rollupOptions at all, so this specific deprecation warning doesn’t fire on this repo’s own build. The rename still applies to any project that does customize it, which is common enough to be worth fixing proactively rather than waiting for a future major version to remove the old key outright. Browse more posts like this in the Guides & Fixes archive.
