This is a die metal 8 layer.

Every iPhone processor that we have dissected has had a Samsung part number on the processor die. We have not found any Samsung markings on the A4 (outside of the DRAM), perhaps the clearest sign to date that Apple is in firm control of the semiconductor design.

We don't expect to find any markings from PA Semi, Apple's recent acquisition, but it's safe to assume they played a major role in designing this package.