the Early Hints were only successfully emitted when I had a proxy_pass in place (like to a backend service), not when Nginx served static files directly from disk.

I suspect the same may be happening in your case: the Link header is set (good), but since there’s no upstream to delay the final response, Nginx just proceeds straight to the full 200 without bothering to emit 103.

`location / {

    add_header Link "</css/main.css>; rel=preload; as=style" early;
	early_hints $http2 $http3;

    proxy_pass http://127.0.0.1:8192;
    proxy_http_version 1.1;
    proxy_set_header Scheme $scheme;
    proxy_set_header Https on;
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header SERVER_PORT $server_port;
    proxy_set_header REMOTE_ADDR $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection $connection_upgrade;
    proxy_read_timeout     120;
    proxy_connect_timeout  120;

}`

the Early Hints were only successfully emitted when I had a proxy_pass in place (like to a backend service), not when Nginx served static files directly from disk.

I suspect the same may be happening in your case: the Link header is set (good), but since there’s no upstream to delay the final response, Nginx just proceeds straight to the full 200 without bothering to emit 103.

`location / {

    add_header Link "</css/main.css>; rel=preload; as=style" early;
	early_hints $http2 $http3;

    proxy_pass http://127.0.0.1:8192;
    proxy_http_version 1.1;
    proxy_set_header Scheme $scheme;
    proxy_set_header Https on;
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header SERVER_PORT $server_port;
    proxy_set_header REMOTE_ADDR $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection $connection_upgrade;
    proxy_read_timeout     120;
    proxy_connect_timeout  120;

}`

Absolutely, it works when Nginx is used as a reverse proxy.

Not sure why 103 doesn't take effect when Nginx serves static sites. For some complex static sites, 103 should have an optimization effect on the loading of blocking resources? Are there any considerations?