After the folks at Anandtech dug deeper into the source code of the new Samsung Galaxy Note 4's Exynos 5433 chipset, they discovered that it uses the new A57/A53 configuration instead of the previous generation Cortex-A15/A7 mashup. ARM themselves have confirmed this to be a 64-bit architecture.
It's odd that Samsung hasn't been touting that fact too loudly and basically only describe the chip as a 1.9 GHz octa-core processor. It is likely that Samsung simply wants to wait until Android L is released because the 64-bit functionality of the chip is mostly useless without a compatible OS to take advantage of it.
Of course, the primary exception to that is that this chipset will support more than 3GB of RAM in a device, but since the Note 4 only comes with 3GB of RAM, there's really no pressure to announce it yet.