
Samsung Galaxy S5 Active
The latest firmware for Samsung Galaxy S5 Active (SM-G870W) is G870WVLU1CPF6 with Android 6.0.1 (Lollipop), released on July 18, 2016 for 8 regions (CSC). Every official firmware build for SM-G870W, 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/G870WVLU1CPF6
SM-G870W started on Android 4 and has received 2 major Android upgrades; it now runs Android 6.0.1 (Lollipop). The newest build, G870WVLU1CPF6, was released on July 18, 2016. No new build has appeared for 125 months, so regular updates for this model have most likely ended.
Specifications of SM-G870A, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-G870F0

SM-G8750

SM-G975WC

SM-G889A

SM-G888N0
The newest firmware for SM-G870W runs Android 6.0.1 (Lollipop): build G870WVLU1CPF6, released on July 18, 2016.
The latest build for SM-G870W, G870WVLU1CPF6, was released on July 18, 2016 (10 years ago).
SM-G870W has had no new firmware for 125 months, so regular updates have most likely ended.
Yes, all firmware files for SM-G870W are 100% official, original, and obtained directly from Samsung servers.
To flash SM-G870W, 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-G870W.