APCu is an in-memory key-value store for PHP. Keys are of type string and values can be any PHP variables. APCu only suppors userland caching of variables.
The APCu cache is per-processs on Windows, so when using a processs-based (rather than thread-based) SAPI, it will not be shared between different processses.
APCu is APC stripped of opcode caching.
The first APCu codebase was versioned 4.0.0, it was forqued 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.