
Samsung Galaxy S 4 (CDMA)
The latest firmware for Samsung Galaxy S 4 (CDMA) (SCH-I959) is I959KEUJPC1 with Android 5.0.1 (Jelly), released on March 22, 2016 for 1 region (CSC). Every official firmware build for SCH-I959, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/I959KEUJPC1
SCH-I959 started on Android 4 and has received 1 major Android upgrade; it now runs Android 5.0.1 (Jelly). The newest build, I959KEUJPC1, was released on March 22, 2016. No new build has appeared for 128 months, so regular updates for this model have most likely ended.

SCH-R970X

SCH-L710

SCH-I939D

SCH-I545PP

SCH-I545L

SCH-I435

SCH-I545

SCH-P709
The newest firmware for SCH-I959 runs Android 5.0.1 (Jelly): build I959KEUJPC1, released on March 22, 2016.
The latest build for SCH-I959, I959KEUJPC1, was released on March 22, 2016 (10 years ago).
SCH-I959 has had no new firmware for 128 months, so regular updates have most likely ended.
Yes, all firmware files for SCH-I959 are 100% official, original, and obtained directly from Samsung servers.
To flash SCH-I959, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing SCH-I959.