Rewrite Not Working in next.config.ts after Upgrade to Next.js 15.2.4

[foylaou]

Summary

I’m encountering an issue after upgrading to Next.js 15.2.4 — the rewrites configuration in next.config.ts no longer works as expected.

Additional information

✅ What Works in 15.0.0

In Next.js 15.0.0, the following next.config.ts setup works correctly. The rewrites are applied properly, and requests to /proxy/* or /app/* are successfully forwarded.

❌ Broken in 15.2.4

After upgrading to 15.2.4, the same rewrites configuration inside next.config.ts stops working. No requests are rewritten, and all traffic to /proxy/* returns 404 or hits default routes.

🧪 Reproduction

The setup uses beforeFiles in a rewrites function, dynamically returning targets based on environment variables:

rewrites: async () => {
  const rules: Rewrite[] = [
    {
      source: "/proxy/:path*",
      destination: `${env.API_URL}/:path*`,
    },
    {
      source: "/app/:path*",
      destination: `${env.RAG_API}/:path*`,
    },
  ];
  return {
    beforeFiles: rules,
  };
}

🔁 Workaround

Converting the configuration file back to next.config.js resolves the issue immediately. The logic and output remain the same — the only change is using JavaScript instead of TypeScript.
📦 Environment
	•	Next.js version: 15.2.4 (broken) / 15.0.0 (works)
	•	Node.js: 18.x
	•	OS: Linux (Docker container)
	•	Config format: next.config.ts
	•	Output mode: standalone
❓Request

Is there any known breaking change related to rewrites in .ts config files since 15.0.0? If not, this might be a regression. Please advise if a change is required in the way next.config.ts should return rewrites in newer versions.

Let me know if a reproduction repo would help — I can publish one if needed.

Thanks for your work on Next.js!

Example

No response

[icyJoseph]

Just adding some work notes while I debug this:

import type { NextConfig } from "next";

const nextConfig: NextConfig = {
  /* config options here */
  async rewrites() {
    const beforeFiles = [
      {
        source: "/proxy/:path*",
        destination: `${process.env.FOO_BAR}/:path*`,
      },
    ];

    return {
      beforeFiles,
    };
  }
};

export default nextConfig;

This next.config.ts yields:

➜ FOO_BAR=http://example.edu yarn dev --port 1234
yarn run v1.22.22
$ next dev --turbopack --port 1234
   ▲ Next.js 15.3.1 (Turbopack)
   - Local:        http://localhost:1234
   - Network:      http://192.168.25.70:1234

 ✓ Starting...
 ✓ Ready in 1885ms
 ○ Compiling / ...
 ✓ Compiled / in 2.5s

Notice, next 15.3.1... and no standalone output mode, which could potentially be the problem, because, IIRC, the config is serialized at some point...

[icyJoseph]

next build and next start also work fine, notice that the route manifest is made during the build time, so example.edu is already included, and won't change during next start

[icyJoseph]

import type { NextConfig } from "next";

const nextConfig: NextConfig = {
  /* config options here */
  output: 'standalone',
  async rewrites() {
    const beforeFiles = [
      {
        source: "/proxy/:path*",
        destination: `${process.env.FOO_BAR}/:path*`,
      },
    ];

    return {
      beforeFiles,
    };
  }
};

export default nextConfig;

Build and then run with:

cp -r public .next/standalone/ && cp -r .next/static .next/standalone/.next/ && node .next/standalone/server.js

Still works fine... in Next 15.3.1... gonna downgrade to 15.2.4 to see what's up.

[icyJoseph]

I can't reproduce on a newly made create-next-app with the rewrite configs I've posted... I even downgraded to 15.2.4, and nothing. We need a reproduction repository from your side.

[foylaou]

I can't reproduce on a newly made create-next-app with the rewrite configs I've posted... I even downgraded to 15.2.4, and nothing. We need a reproduction repository from your side.

Thank you for looking into this. I’ve just sent the reproduction repository to your email — please check your inbox.

[icyJoseph]

Ty, I've run out of time to look at these this morning. I'll try to take a look later today.

[x0y-gt]

I have the same issue with v15.2