
Samsung Galaxy S 4 (Exynos Octa)
The latest firmware for Samsung Galaxy S 4 (Exynos Octa) (GT-I9500) is I9500ZCUJQD1 with Android 5.0.1 (Jelly), released on April 19, 2017 for 1 region (CSC). Every official firmware build for GT-I9500, 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/I9500ZCUJQD1
GT-I9500 started on Android 4 and has received 1 major Android upgrade; it now runs Android 5.0.1 (Jelly). The newest build, I9500ZCUJQD1, was released on April 19, 2017. No new build has appeared for 115 months, so regular updates for this model have most likely ended.
Box codes of GT-I9500 for different colors and markets. Firmware is chosen by the model code GT-I9500 and your region (CSC), not by the SKU.

GT-I9308

GT-I9268

GT-I9228

GT-I9210

GT-I9108
The newest firmware for GT-I9500 runs Android 5.0.1 (Jelly): build I9500ZCUJQD1, released on April 19, 2017.
The latest build for GT-I9500, I9500ZCUJQD1, was released on April 19, 2017 (9 years ago).
GT-I9500 has had no new firmware for 115 months, so regular updates have most likely ended.
Yes, all firmware files for GT-I9500 are 100% official, original, and obtained directly from Samsung servers.
To flash GT-I9500, 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 GT-I9500.