`next-router-prefetch` header missing on some prefetch requests

[salazarm]

Link to the code that reproduces this issue

https://github.com/salazarm/nextjs-missing-prefetch-header/tree/main/nextjs-missing-prefetch-header

To Reproduce

1. Build the repo app npm run dev and start it npm run start.

2. Observe in the network panel that we're prefetching the same url twice, once with the next-router-prefetch header set and once without.

   From the guide here:
   I'm using:

 missing: [
        { type: 'header', key: 'next-router-prefetch' },
        { type: 'header', key: 'purpose', value: 'prefetch' },
      ],

But since sometimes the prefetch doesn't include next-router-prefetch we end up including the CSP on those and in my case the CSP is 7kb and we make a lot of prefetch requests so it adds up quickly.

Current vs. Expected behavior

1. I expected all prefetch requests to include the next-router-prefetch header
2. I expect to only prefetch the 123 route once.

Provide environment information

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 25.0.0: Wed Sep 17 21:41:26 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T6041
  Available memory (MB): 49152
  Available CPU cores: 14
Binaries:
  Node: 22.19.0
  npm: 10.9.3
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 16.0.1 // Latest available version is detected (16.0.1).
  eslint-config-next: N/A
  react: 19.2.0
  react-dom: 19.2.0
  typescript: 5.9.3
Next.js Config:
  output: N/A

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

Not sure, Dynamic Routes

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

next build (local), Vercel (Deployed)

Additional context

No response

[ztanner]

Hi @salazarm -

prefetch={true} is technically not distinguishable between a prefetch request and a regular page navigation - setting this property to true tells Next.js to fetch the full page information. Omitting the prop doesn't mean Next.js won't prefetch the page, it just will avoid invoking potentially expensive API calls if the target page was not a fully static page.

The request that you're seeing that is omitting the header comes from this link. If you omitted prefetch={true}, all requests would contain the prefetch header.

[salazarm]

@ztanner What about the duplicate prefetching? In my own production app I'm seeing the same prefetches being made multiple times.

[ztanner]

@salazarm this was part of the Next.js 16 release described in the blog notes, specifically the routing section here. The relevant section is:

Trade-off: You may see more individual prefetch requests, but with much lower total transfer sizes. We believe this is the right trade-off for nearly all applications. If the increased request count causes issues, please let us know. We're working on additional optimizations to inline data chunks more efficiently.

We'll likely expose some configuration to customize this further, but wanting to clarify that the increase in prefetches is expected at the moment when using Next 16.