Home route "/" is also accessible via "/index" automatically on Vercel

[mikkeldamm]

Link to the code that reproduces this issue

https://github.com/mikkeldamm/home-index-route

To Reproduce

The issue only exists on Vercel, but if you visit this url:
https://home-index-route.vercel.app/
And this url:
https://home-index-route.vercel.app/index

Then they are the same route, but nothing in the application is setup to listen for "index"

The issue exist in both the app and pages router

Current vs. Expected behavior

I would expect the /index route to return 404 like it does when running next dev or next build && next start (locally)

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.6.0: Mon Jul 14 11:30:51 PDT 2025; root:xnu-11417.140.69~1/RELEASE_ARM64_T8112
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 23.11.0
  npm: 10.9.2
  Yarn: 1.22.19
  pnpm: 10.3.0
Relevant Packages:
  next: 16.0.10 // Latest available version is detected (16.0.10).
  eslint-config-next: N/A
  react: 19.2.1
  react-dom: 19.2.1
  typescript: 5.9.3
Next.js Config:
  output: N/A

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

Linking and Navigating

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

Vercel (Deployed)

Additional context

No response