Hi everyone,

I've noticed that Next.js doesn't gzip API route responses even when the Accept-Encoding: gzip header is included in the request. Here's what I've tested so far:

Environment:

Next.js versions: 14.1.0 and 15.0.4
Simple API route under the App Router, returning a JSON payload larger than 1KB.
Using curl to send requests with Accept-Encoding: gzip.
Issue:

Static files are gzipped as expected, but API route responses are not gzipped.
The Content-Encoding: gzip header is missing, and the response size remains uncompressed.
Reproduction Steps:

Create a simple API route:

export async function GET() {
    const data = Array(5000).fill({ id: 1, name: "example" });
    return new Response(JSON.stringify(data), {
        headers: { "Content-Type": "application/json" },
    });
}

Start the application in development mode using next dev. Send a GET request using:curl -H "Accept-Encoding: gzip" http://localhost:3000/api/example`

Observe that the Content-Encoding header is missing, and the response size is uncompressed.

Question: Does Next.js rely on external tools like Nginx or a CDN for gzip compression in API routes? Or is there a built-in way to enable gzip compression for API responses?

https://github.com/vercel/next.js/issues/73695