According to the Raspberry Pi Foundation, almost 3 million Raspberry Pi 4 units have been sold so far. When it was first released, the team faced limitations that capped the memory capacity at 4 GB.
The Pi 4 uses a BCM2711 chip that can address a maximum of 16 GB of LPDDR4 SDRAM, but without the right package, the Pi can't make use of it. A company known as Micron released an 8 GB LPDDR4 package earlier this year, giving the Raspberry Pi Foundation team an opportunity to develop the 8 GB Raspberry Pi 4 model.
The new upgrade required small changes to the board hardware to support the new peak current requirements, including complete relocation of the switch-mode power supply and the addition of a new switcher.
If you want to get your hands on the new 8 GB model, good news! It's available to purchase now for $75 (USD). Check out the product page on the official Raspberry Pi website for more details.