APCu is an in-memory key-value store for PHP. Keys are of type string and values can be any PHP variables. APCu only supports userland caching of variables.
The APCu cache is per-process on Windows, so when using a process-based (rather than thread-based) SAPI, it will not be shared between different processes.
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.