Representatives of the Raspberry Pi Foundation have announced on their blog that the Compute Module 4 is now ready for sale starting at $25. The system-on-module variant of the Raspberry Pi 4 runs the same 64-bit quad-core BCM2711 application processor.
Raspberry Pi Compute modules exist since the RP2. To be able to prototype with this module, you need the RP "motherboard" that add all rhe extra hardwzre, such as power port, usb, lan audio and video, etc.