
Samsung GALAXY S Ⅲ
The latest firmware for Samsung GALAXY S Ⅲ (SGH-T999) is T999UVDLJC with Jelly(Android Bean), released on January 16, 2013 for 1 region (CSC). Every official firmware build for SGH-T999, 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/T999UVDLJC
All 6 builds in our database run Android 4.3 (Jelly). The newest build, T999UVDLJC, was released on January 16, 2013. No new build has appeared for 167 months, so regular updates for this model have most likely ended.

SGH-I927

SGH-S730M

SGH-T999N

SGH-T989D

SGH-T859

SGH-T599V

SGH-I757M

SGH-I747
The newest firmware for SGH-T999 runs Android 4.3 (Jelly): build T999UVDLJC, released on January 16, 2013.
The latest build for SGH-T999, T999UVDLJC, was released on January 16, 2013 (13 years ago).
SGH-T999 has had no new firmware for 167 months, so regular updates have most likely ended.
Yes, all firmware files for SGH-T999 are 100% official, original, and obtained directly from Samsung servers.
To flash SGH-T999, 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 SGH-T999.