icurdinj

If you want to enable your WordPress site to send HTTP 103 Early Hints header, you can do so by installing this plugin.
It will: 
1. Check if the server supports HTTP 103 Early Hints. 
2. If it does, the plugin will prepare everything needed to send the header.
Right now, this plugin supports recent versions of Apache web server – 2.4.58 and newer, and FrankenPHP web server – 
v1.2 and newer.
Also, your site needs to be served over HTTP/2 protocol. (If it’s not, the browsers would ignore the header.)
<h3>License</h3>
This plugin is free software: you can redistribute it and/or modify 
it under the terms of the GNU General Public License as published by 
the Free Software Foundation, either version 2 of the License, or 
(at your option) any later version.
This plugin is distributed in the hope that it will be useful, 
but WITHOUT ANY WARRANTY; without even the implied warranty of 
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 
GNU General Public License for more details.
You should have received a copy of the GNU General Public License 
along with this plugin. If not, see <a href="https://www.gnu.org/licenses/" rel="nofollow ugc">https://www.gnu.org/licenses/</a>.

Easy HTTP 103

Improves the speed of your site by sending HTTP 103 Early Hints header.

Easy HTTP 103 vs Jetpack – WP Security, Backup, Speed, & Growth