App Router: returning notFound() from generateMetadata does not change the response status code to 404 if there's a loading.tsx component

[felipedeboni]

Link to the code that reproduces this issue

https://github.com/felipedeboni/next-404

To Reproduce

Go to: https://next-404-ten.vercel.app/with-loading

• not found is rendered
• response status is 200 OK.

Go to: https://next-404-ten.vercel.app/with-parent-loading

• renders the page as expected.

Go to: https://next-404-ten.vercel.app/with-parent-loading/children

• not found is rendered
• response status is 200 OK.

Current vs. Expected behavior

When returning notFound from generateMetadata I would expect the response to have a 404 Not Found status in order to allow pages to be removed from Google Index and others...

The alternative is awful, in middleware:

• Check if it's a bot. If not just continue.
• Check if resource exists. If it does continue.
• Send 404 Not Found.

However this is going to make things slower for bots, making the web vitals score lower given there's no fetch cache on middleware and fetch calls made on middleware aren't shared (cached) with the page itself.

For regular access I it's fine to have 200 OK and just show not found component (or default), however for bots we need the proper status.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.2.0: Fri Dec  6 18:56:34 PST 2024; root:xnu-11215.61.5~2/RELEASE_ARM64_T6020
  Available memory (MB): 65536
  Available CPU cores: 12
Binaries:
  Node: 20.9.0
  npm: 10.1.0
  Yarn: 1.22.21
  pnpm: 9.4.0
Relevant Packages:
  next: 15.1.6 // Latest available version is detected (15.1.6).
  eslint-config-next: 15.1.6
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Loading UI and Streaming, Metadata

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local), next start (local), Vercel (Deployed)

Additional context

No response