The Amazon Kindle Paperwhite (2024, 12th generation) is delivered with the latest version of the Kindle OS, which is up to date with production and delivery at the start of sales.
The exact pre-installed version is: Kindle OS 5.17.1
This is a 64-bit version of the operating system that is specially optimised for the new generation of hardware and supports all the new functions of the device.
Important note:
After setting up and connecting to a Wi-Fi network for the first time, the Kindle usually downloads and installs important software updates immediately to get the latest version (e.g. 5.17.1.1 or newer).