What is the difference between Saturn 4 Ultra and Ultra 16K?

The short version: Saturn 4 Ultra 16K is the finer-detail version; Saturn 4 Ultra is the better value if you do not need the highest LCD resolution.

Both are resin MSLA printers in the same Elegoo Saturn 4 Ultra family, so they are aimed at similar users: miniatures, figures, jewelry-like detail, and high-resolution resin printing. The main practical difference is the screen: the Ultra 16K uses a higher-resolution LCD, which can produce slightly finer XY detail, while the standard Saturn 4 Ultra is already very detailed and may be cheaper or easier to justify for everyday printing.

Choose Saturn 4 Ultra 16K if you print tiny text, sharp miniatures, display models, or detail-critical parts and want the newest/highest-resolution option. Choose Saturn 4 Ultra if you want most of the same workflow features and print quality but care more about price-to-performance.