Another rumor is that instead of its usual AMOLED screen which contained green and blue fluorescent OLEDs and the red OLEDs were phosphorescent, Samsung will use phosphorescent materials for the red and green OLEDs, and fluorescent materials for the blue ones. This so-called Green PHOLED display is 25% more power efficient than an AMOLED screen with nothing major changed in the term of the quality of the picture.
There is speculation about two prototypes of the Samsung Galaxy S 4. One has an LCD display and uses a Qualcomm Snapdragon 600 processor while the other has an AMOLED screen and features the Samsung Exynos 5 Octa processor. At this point, it is unknown whether Samsung plans on selling both models depending on the region, or if one of the two will be dropped before next week's introduction of the phone in New York.
One last note. Android 4.2.1 will be on the device at launch with an update to 4.2.2 coming the same month as the phone's launch.
source: SamMobile, OLED-Info.com via AndroidAuthority