TypeScript version

A knext create-scaffolded app pins typescript@^5.9.3. This page explains why that's the default, what TypeScript 7 actually gets you, and how to opt in if you want it anyway.

The default: TypeScript 5.9.x

TypeScript 7 is the new Go-native compiler, and it's real: a scaffolded app builds and runs its tests cleanly under it on either build target, and Next.js's own typecheck step during next build works correctly under TS7 (verified directly: a scaffolded app builds clean, 0 errors) — it needs none of the classic TypeScript compiler API.

It is not the default anyway, because of one real gap: TypeScript 7 ships no tsserver.js. That's the specific protocol editors like VS Code speak when you tell them to "use the workspace version" of TypeScript — inline errors, autocomplete, go-to-definition, and the next tsconfig plugin all go through it. TS7 does have a language server (tsc --lsp --stdio, a JSON-RPC LSP implementation), but it's a different protocol than tsserver.js — an editor extension built around "use workspace version" doesn't pick it up automatically, so it breaks until editor tooling catches up.

Nothing else about a scaffolded app needs the change flagged: it ships no linter (no eslint, no lint script, no eslint-config-next), so there's no lint-toolchain breakage to speak of.

Opting in to TypeScript 7

If you don't need editor TypeScript support (for example, a CI-only build, or you're comfortable running without it until editor tooling catches up), you can switch a scaffolded app to TS7 yourself:

{
  "devDependencies": {
-   "typescript": "^5.9.3",
+   "typescript": "^7.0.2"
  }
}

Reinstall after changing it. next build's own typecheck step and your app's own type-checking will keep working. What you lose the moment you do this:

• Editor inline type errors, autocomplete, and go-to-definition for TypeScript files that rely on "use workspace version" — your editor falls back to its own bundled TypeScript (which may not understand next.config.ts's types the same way), or errors trying to start tsserver.js.

If you hit that and want it back, pin typescript back to ^5.9.3 and reinstall — nothing else about your app changes either way.