G991USQSHHYI1 – Galaxy S21 5G firmware
Build G991USQSHHYI1 is a security update for the Galaxy S21 5G (SM-G991U)
on Android 15 (One UI 7). It first appeared on Samsung's servers on Sep 24, 2025 (method) and has reached
8 regions so far. It raises the bootloader bit from 16 to 17: once installed, the device no longer accepts firmware with bit 16 or lower, so a downgrade to G991USQSGHYF2 is blocked. Samsung still serves this file.
- Model
- SM-G991U
- Android
- Android 15
- Type
- Security
- Bootloader bit
- 17
- First released
- Sep 24, 2025
- Regions
- 8
Rollout timeline by region
The date each region code (CSC) first received G991USQSHHYI1, counted from the first release.
| CSC | Region | Released | Rollout | Version (PDA/CSC/MODEM) |
|---|---|---|---|---|
ATT | USA (AT&T) | Sep 24, 2025 | day 0 | G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1 |
DSA | USA | Sep 26, 2025 | +2 days | G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1 |
DSH | USA | Sep 26, 2025 | +2 days | G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1 |
CCT | USA (Comcast) | Sep 28, 2025 | +4 days | G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1 |
SPR | USA (Sprint) | Sep 28, 2025 | +4 days | G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1 |
TMB | USA (T-Mobile) | Sep 28, 2025 | +4 days | G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1 |
VZW | USA (Verizon) | Sep 29, 2025 | +5 days | G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1 |
USC | USA (US Cellular) | Oct 6, 2025 | +12 days | G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1 |
Download and release notes
samloader download -m SM-G991U -r ATT -v G991USQSHHYI1/G991UOYNHHYI1/G991USQSHHYI1Samsung's release notes and security patch level for this update: SM-G991U / ATT on doc.samsungmobile.com. What each part of the build number means: decode G991USQSHHYI1.