APCu is the official replacement for the outdated APC extension. APC provided both opcode caching (opcache) and object caching. As PHP versions 5.5 and above include their own opcache, APC was no longer compatible, and its opcache functionality became use
APCu is APC stripped of opcode caching. The first APCu codebase was versioned 4.0.0, it was forked from the head of the APC master branch at the time. PHP 7 support is available as of APCu 5.0.0. PHP 8 support is available as of APCu 5.1.19.