With one of the latest Broadcom 2711; Quad-Core Cortex A72 (ARM V8-A) 64-bit SoC Clocked at 1.8GHz processor.
The latest 5.0 Bluetooth allows you to use Bluetooth devices with more range than before without extra dongles; keeping things nice and tidy.
The GPIO header remains the same, with 40 pins; fully backward-compatible with previous boards as on the previous three models of Pi. However; it should note that the new PoE header pins may contact components on the underside of some HATs; like Rainbow HAT. Some standoffs will prevent any mischief from occurring though!