
Samsung Galaxy S3
The latest firmware for Samsung Galaxy S3 (GT-I9305T) is I9305TDVBME2 with Jelly(Android Bean), released on May 13, 2013 for 1 region (CSC). Every official firmware build for GT-I9305T, 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/I9305TDVBME2
All 14 builds in our database run Android 4.4.4 (Jelly). The newest build, I9305TDVBME2, was released on May 13, 2013. No new build has appeared for 163 months, so regular updates for this model have most likely ended.

GT-I9308

GT-I9268

GT-I9228

GT-I9210

GT-I9108
The newest firmware for GT-I9305T runs Android 4.4.4 (Jelly): build I9305TDVBME2, released on May 13, 2013.
The latest build for GT-I9305T, I9305TDVBME2, was released on May 13, 2013 (13 years ago).
GT-I9305T has had no new firmware for 163 months, so regular updates have most likely ended.
Yes, all firmware files for GT-I9305T are 100% official, original, and obtained directly from Samsung servers.
To flash GT-I9305T, 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-I9305T.