
Samsung Galaxy Alpha
The latest firmware for Samsung Galaxy Alpha (SM-G850W) is G850WVLU1BPG1 with Android 5.0.2 (Lollipop), released on July 26, 2016 for 11 regions (CSC). Every official firmware build for SM-G850W, 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/G850WVLU1BPG1
SM-G850W started on Android 4 and has received 1 major Android upgrade; it now runs Android 5.0.2 (Lollipop). The newest build, G850WVLU1BPG1, was released on July 26, 2016. No new build has appeared for 124 months, so regular updates for this model have most likely ended.
Specifications of SM-G850F, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-G850X

SM-G950FD

SM-G955FD

SM-G860P

SM-G750H
The newest firmware for SM-G850W runs Android 5.0.2 (Lollipop): build G850WVLU1BPG1, released on July 26, 2016.
The latest build for SM-G850W, G850WVLU1BPG1, was released on July 26, 2016 (10 years ago).
SM-G850W has had no new firmware for 124 months, so regular updates have most likely ended.
Yes, all firmware files for SM-G850W are 100% official, original, and obtained directly from Samsung servers.
To flash SM-G850W, 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-G850W.