Preloading is a production setting with a restart cost

7.4 can compile a set of files once at server start and keep them in memory permanently, skipping the per-request opcache lookup entirely.

; php.ini
opcache.preload=/var/www/app/preload.php
opcache.preload_user=www-data

; preload.php
; <?php
; $files = require __DIR__ . '/vendor/composer/autoload_classmap.php';
; foreach ($files as $file) { opcache_compile_file($file); }

The catch is that preloaded files are fixed until php-fpm restarts, so a deploy is a restart rather than a reload — and a restart drops in-flight requests unless something drains them first. It also fails loudly at start on any file with an unresolvable dependency, which is a good failure and means the preload script needs curating rather than pointing at everything. The measured gain on a framework application is real but modest, in the range of a few percent, and it is not the reason to upgrade.