Xiaomi 12S Ultra (codename thor) is a flagship camera-centric phone powered by Snapdragon 8+ Gen 1 and built around a large 1-inch main camera sensor concept. Despite its premium hardware, owners commonly run into software-side pain points such as abnormal battery drain after major updates, overheating under certain usage patterns, and “stuck in Fastboot / soft-brick” situations after failed flashing or mismatched ROM attempts.
Installing the correct official firmware fastboot package (OS1.0.16.0.ULACNXM) helps restore a clean system state, repair corrupted partitions, and stabilize performance when the device is affected by update failures, bootloops, or system instability.
Xiaomi 12S Ultra (thor) Firmware Details
| Device name | Xiaomi 12S Ultra |
|---|---|
| Codename | thor |
| Model identifier | 2203121C |
| Chipset (SoC) | Qualcomm SM8475 Snapdragon 8+ Gen 1 |
| Android version (official fastboot) | Android 14 (per build name) |
| Official firmware version | OS1.0.16.0.ULACNXM (China / CNXM) |
| Build date (from filename) | 2024-12-24 |
| File type | Fastboot ROM (.tgz) / stock firmware package |
| Flashing tool required | Xiaomi Mi Flash Tool (Fastboot mode) |
| Bootloader status | Fastboot flashing commonly requires an unlocked bootloader on Xiaomi devices. |
| Region note | Xiaomi 12S Ultra is primarily a China-market device and is widely reported to have no official Global ROM branch. |
⚠️ Flashing Risks & Disclaimer
- Flashing firmware on Xiaomi 12S Ultra (thor / 2203121C) is an advanced procedure with a real risk of permanent damage.
- Using the wrong ROM/region (CNXM mismatch), mixed builds, incorrect scripts, or an interrupted flash may cause hard-brick, bootloops, endless fastboot, complete data loss, partition corruption, radio issues, system instability, security problems, and warranty/service complications.
- All stock ROM downloads, custom ROM links, recovery images, and instructions are provided “as is”, without any warranties (express or implied), and no liability is accepted for damage, malfunction, or lost data.
- Before proceeding: confirm codename = thor, confirm the exact target build (ULACNXM / CNXM), back up data, and ensure the flashing steps are fully understood.
- Continuing means full responsibility for all outcomes resulting from flashing.
Download Official Firmware for Xiaomi 12S Ultra (thor)
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| Filename | File size | Build date | Build / version | Android | Flashing type | Download link |
|---|---|---|---|---|---|---|
| thor_images_OS1.0.16.0.ULACNXM_20241224.0000.00_14.0_cn_481a059036.tgz | 6.97GB | 2024-12-24 | OS1.0.16.0.ULACNXM (China / CNXM) | 14.0 | Fastboot ROM (.tgz) | Download OS1.0.16.0 ULACNXM (Xiaomi Big OTA) |
| xiaomi.eu_THOR_OS2.0.212.0.VLACNXM_15.zip | 5.57GB | (Varies by release) | xiaomi.eu HyperOS 2.0.212.0.VLACNXM | 15 | Custom ROM ZIP (requires unlocked bootloader + custom flashing method) | Download HyperOS 2.0.212.0 (SourceForge) |
| twrp-3.7.1_12-v9.0_A15-thor-skkk.img | 100MB | (Recovery image) | TWRP 3.7.1 (thor) | N/A | Custom recovery (.img) (advanced / bootloader unlock required) | Download TWRP for thor (SourceForge) |
Flashing Requirements
- A Windows PC, stable USB cable/port, and enough disk space to extract the TGZ fastboot ROM.
- Xiaomi Mi Flash Tool installed (fastboot flashing workflow for Xiaomi devices).
- Unlocked bootloader (commonly required for fastboot flashing and custom recovery/ROM workflows).
- A complete backup (fastboot flashing often wipes data depending on selected options and device state).
- Correct device matching: Xiaomi 12S Ultra must be thor and the official build must match ULACNXM/CNXM to avoid cross-branch issues.
How to Flash the Firmware
Method A: Official Fastboot ROM (Mi Flash Tool)
- Extract the thor_images_….tgz package until the fastboot ROM folder and flash scripts are visible.
- Boot Xiaomi 12S Ultra (thor) into Fastboot mode and connect it to the PC.
- Open Xiaomi Mi Flash Tool, select the extracted ROM folder, and refresh to detect the device.
- Choose the appropriate flash option (data-wipe options may apply), then start flashing and do not disconnect.
- Reboot and allow extra time for the first boot after reinstalling the official firmware.
Method B: flash_all Script (Fastboot Script Flashing)
- Extract the TGZ fastboot ROM and locate the included flash scripts (commonly “flash_all”).
- Connect the phone in Fastboot mode and confirm the PC detects it.
- Run the script and wait until flashing completes.
- Do not interrupt the process to reduce the risk of partition corruption or hard-brick.
- Reboot and complete setup (a wipe may occur depending on the chosen method/options).
Step-by-step guides (pictures & videos):
- Xiaomi MI Flash Tool guide (recommended for OS1.0.16.0.ULACNXM)
- Flash.bat / fastboot script guide (advanced)
Frequently Asked Questions (FAQs)
What phone model is “thor” firmware for?
Thor is the device codename for Xiaomi 12S Ultra, commonly associated with model 2203121C.
Is OS1.0.16.0.ULACNXM a stock ROM?
Yes, OS1.0.16.0.ULACNXM is an official firmware build distributed as a fastboot ROM, often searched as stock ROM, stock firmware, or flash file for Xiaomi 12S Ultra (thor).
Does Xiaomi 12S Ultra (thor) have an official Global ROM?
Xiaomi 12S Ultra (thor) is widely described as not sold outside China and therefore not having an official Global ROM branch, which makes correct CNXM matching especially important.
Can official firmware fix camera lens fog/condensation on Xiaomi 12S Ultra?
Lens fog/condensation is generally discussed as a physical phenomenon rather than a software bug, so flashing official firmware is not a guaranteed fix for that specific problem.
Why do bootloops or “stuck in Fastboot” happen after flashing on thor?
Community reports show that using mismatched builds or making mistakes during custom flashing can leave Xiaomi 12S Ultra stuck in Fastboot mode and require restoring a proper fastboot ROM.
