
Samsung GALAXY S5
The latest firmware for Samsung GALAXY S5 (SM-G900AZ) is G900AZTUS3BQD1 with Android 5.0 (Lollipop), released on April 10, 2017 for 1 region (CSC). Every official firmware build for SM-G900AZ, 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/G900AZTUS3BQD1
All 10 builds in our database run Android 5.0 (Lollipop). The newest build, G900AZTUS3BQD1, was released on April 10, 2017. No new build has appeared for 116 months, so regular updates for this model have most likely ended.
Specifications of SM-G900, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-G900FG

SM-G9098

SM-G906S

SM-G903W

SM-G901F
The newest firmware for SM-G900AZ runs Android 5.0 (Lollipop): build G900AZTUS3BQD1, released on April 10, 2017.
The latest build for SM-G900AZ, G900AZTUS3BQD1, was released on April 10, 2017 (9 years ago).
SM-G900AZ has had no new firmware for 116 months, so regular updates have most likely ended.
Yes, all firmware files for SM-G900AZ are 100% official, original, and obtained directly from Samsung servers.
To flash SM-G900AZ, 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 SM-G900AZ.