A significant upgrade was made to the ‘z’ axis of the printer. The “S” uses a dual guide system and much stronger components, which makes the z axis a lot more stable than the original model. Another upgrade is the UV LED is more powerful, meaning shorter exposures and faster print times. The original Photon has a 25w LED array, where the S is 38w.

https://www.amazon.com/ANYCUBIC-Photon-Upgraded-Off-line-Printing/dp/B07RY6NSL8