CAS is not integer on the PHP client SDK 3.0

Hello,

In PHP client when I get a CAS from a getAndLock operation the CAS looks like AAB4Ol5dKRY= instead of an integer.

I am getting the CAS using:

$res = $collection->getAndLock("docId" , 1 0);
$lockedCas = $res->cas();

How can I get the integer value for CAS?