
Samsung Galaxy S 3 (China)
The latest firmware for Samsung Galaxy S 3 (China) (GT-I9308) is I9308ZMUBNI1 with Android 4.3 (Jelly), released on September 28, 2014 for 1 region (CSC). Every official firmware build for GT-I9308, 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/I9308ZMUBNI1
All 3 builds in our database run Android 4.3 (Jelly). The newest build, I9308ZMUBNI1, was released on September 28, 2014. No new build has appeared for 146 months, so regular updates for this model have most likely ended.

GT-I9268

GT-I9228

GT-I9210

GT-I9108

GT-I9103

GT-I9100T

GT-I9050

GT-I9008L
The newest firmware for GT-I9308 runs Android 4.3 (Jelly): build I9308ZMUBNI1, released on September 28, 2014.
The latest build for GT-I9308, I9308ZMUBNI1, was released on September 28, 2014 (12 years ago).
GT-I9308 has had no new firmware for 146 months, so regular updates have most likely ended.
Yes, all firmware files for GT-I9308 are 100% official, original, and obtained directly from Samsung servers.
To flash GT-I9308, 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-I9308.