diff --git a/vike/node/api/build.ts b/vike/node/api/build.ts
index 98c2225712..a4afd0a9f3 100644
--- a/vike/node/api/build.ts
+++ b/vike/node/api/build.ts
@@ -1,11 +1,12 @@
 export { build }
 
 import { prepareViteApiCall } from './prepareViteApiCall.js'
-import { build as buildVite, createBuilder } from 'vite'
+import { build as buildVite, version } from 'vite'
 import type { APIOptions } from './types.js'
 import assert from 'assert'
 import { isVikeCli } from '../cli/context.js'
 import { isPrerendering } from '../prerender/context.js'
+import { assertVersion } from '../../utils/assertVersion.js'
 
 /**
  * Programmatically trigger `$ vike build`
@@ -26,6 +27,8 @@ async function build(options: APIOptions = {}): Promise<{}> {
   //    > We purposely don't start the pre-rendering in this `build()` function but in a Rollup hook instead.
   //    > Rationale: https://github.com/vikejs/vike/issues/2123
   if (vikeConfig.global.config.viteEnvironmentAPI) {
+    assertVersion('Vite', version, '6.0.0')
+    const { createBuilder } = await import('vite')
     const builder = await createBuilder(viteConfigEnhanced)
     await builder.buildApp()
   } else {
diff --git a/vike/node/plugin/plugins/buildConfig.ts b/vike/node/plugin/plugins/buildConfig.ts
index 00dff47707..b4e687cfe0 100644
--- a/vike/node/plugin/plugins/buildConfig.ts
+++ b/vike/node/plugin/plugins/buildConfig.ts
@@ -36,7 +36,7 @@ import { prependEntriesDir } from '../../shared/prependEntriesDir.js'
 import { getFilePathResolved } from '../shared/getFilePath.js'
 import { getConfigValueBuildTime } from '../../../shared/page-configs/getConfigValueBuildTime.js'
 import { getOutDirs, type OutDirs, resolveOutDir } from '../shared/getOutDirs.js'
-import { viteIsSSR } from '../shared/viteIsSSR.js'
+import { vite6IsSSR, viteIsSSR } from '../shared/viteIsSSR.js'
 // @ts-ignore Shimmed by dist-cjs-fixup.js for CJS build.
 const importMetaUrl: string = import.meta.url
 const require_ = createRequire(importMetaUrl)
@@ -109,7 +109,7 @@ function buildConfig(): Plugin[] {
         order: 'pre',
         sequential: true,
         async handler(options, bundle) {
-          if (isSsrBuild || this.environment.name === 'ssr') {
+          if (isSsrBuild || vite6IsSSR(this)) {
             console.log('FIXING SERVER ASSETS')
             // Ideally we'd move dist/_temp_manifest.json to dist/server/client-assets.json instead of dist/assets.json
             //  - But we can't because there is no guarentee whether dist/server/ is generated before or after dist/client/ (generating dist/server/ after dist/client/ erases dist/server/client-assets.json)
diff --git a/vike/node/plugin/shared/viteIsSSR.ts b/vike/node/plugin/shared/viteIsSSR.ts
index e996c0e4c3..8f2c7e8e01 100644
--- a/vike/node/plugin/shared/viteIsSSR.ts
+++ b/vike/node/plugin/shared/viteIsSSR.ts
@@ -2,12 +2,17 @@ import { assert } from '../../../utils/assert.js'
 import { isObject } from '../../../utils/isObject.js'
 
 export { viteIsSSR }
+export { vite6IsSSR }
 export { viteIsSSR_options }
 
 function viteIsSSR(config: { build?: { ssr?: boolean | string } }): boolean {
   return !!config?.build?.ssr
 }
 
+function vite6IsSSR<T extends { environment: { name: string } }>(self: T): boolean {
+  return 'environment' in self && self.environment.name === 'ssr'
+}
+
 type Options = undefined | boolean | { ssr?: boolean }
 // https://github.com/vitejs/vite/discussions/5109#discussioncomment-1450726
 function viteIsSSR_options(options: Options): boolean {