Description:

APCu is userland caching: APC stripped of opcode caching in
preparation for the deployment of Zend Optimizer+ as the primary
solution to opcode caching in future versions of PHP.

APCu only supports userland caching (and dumping) of variables,
providing an upgrade path for the future. When O+ takes over, many
will be tempted to use 3rd party solutions to userland caching,
possibly even distributed solutions; this would be a grave error. The
tried and tested APC codebase provides far superior support for local
storage of PHP variables.