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.)
License
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 https://www.gnu.org/licenses/.