The raspberry Pi foundation loves it surprises and just as they did with the Raspberry Pi 3 when they first announced it the Raspberry Pi 4 is available for purchase on the same day :).
From the reviews I have read so far there is a trade off of slightly more power consumption for at-least double the performance of the Pi 3. There is also massive I/O performance gains. See the new specs below.
|SOC||Broadcom BCM2711B0 quad-core A72 (ARMv8-A) 64-bit @ 1.5GHz|
|GPU||Broadcom VideoCore VI|
|RAM||1GB, 2GB, or 4GB LPDDR4 SDRAM|
|Bluetooth||Bluetooth 5.0, Bluetooth Low Energy (BLE)|
|GPIO||40-pin GPIO header, populated|
|Ports||2 × micro-HDMI 2.0, 3.5 mm analogue audio-video jack, 2 × USB 2.0, 2 × USB 3.0, Gigabit Ethernet, Camera Serial Interface (CSI), Display Serial Interface (DSI)|
|Dimentions||88 mm × 58 mm × 19.5 mm, 46 g|
Here are some informative links