Xiaomi MIX 4 Review: Features & Specs Uncovered

Xiaomi MIX 4 (2021) – Comeback with Under-Display Camera (UDC/CUP)

Overview

The Xiaomi MIX 4 (Model: 2106118C) is the long-awaited return of the iconic MIX series (after a 3-year hiatus since MIX 3 in 2018), unveiled on August 10, 2021, and released on August 16, 2021. It marked Xiaomi’s first flagship to feature a true under-display camera (UDC/CUP Camera Under Panel)—ditching notches, punch – holes, or mechanical sliders for an unbroken full – screen experience, paired with a premium ceramic back, flagship Snapdragon 888+ chip, and 120W fast charging. Launched with Android 11 (MIUI 12.5), it offered 3 years of OS updates and 4 years of security patches, targeting tech enthusiasts craving innovation and a “bezel – less” aesthetic. Its core value lies in balancing cutting – edge UDC tech with flagship – grade performance and charging, redefining Xiaomi’s premium design language.

Key Technical Specifications

Category	Details
Display	6.67 – inch curved AMOLED (2400×1080, 395ppi); 120Hz refresh rate, 480Hz touch sampling rate; Gorilla Glass Victus; UDC (CUP) with customized sub – pixel matrix; ~87.6% screen – to – body ratio; 1000 nits peak brightness; HDR10+ support
Processor	Qualcomm Snapdragon 888+ 5G (5nm, octa – core: 1×2.99GHz Cortex – X1 + 3×2.42GHz Cortex – A78 + 4×1.80GHz Cortex – A55); Adreno 660 GPU
Memory & Storage	8GB/12GB LPDDR5 RAM; 128GB/256GB/512GB UFS 3.1 storage (non – expandable); Dual – SIM (Nano – SIM, dual – standby)
Camera System	– Rear Triple: 108MP wide (f/1.9, 1/1.33″, PDAF, Laser AF, OIS); 8MP periscope telephoto (f/4.1, 5x optical zoom, OIS); 13MP ultrawide (f/2.2, 123° FOV)- Front UDC: 20MP (0.8μm pixels, customized pixel layout for light transmission); supports 1080p video calls
Battery & Charging	4500mAh Li – Po (non – removable); 120W wired (100% charge in ~15 mins), 50W wireless, 10W reverse wireless; no removable battery
Design & Build	Oxide zirconia ceramic back, aluminum frame; 162.6×75.4×8.0mm; Weight: 225g; IP53 dust/water resistance; In – display optical fingerprint
Connectivity	5G Sub – 6 GHz; Wi – Fi 6 (802.11ax); Bluetooth 5.2; NFC; UWB (Ultra – Wideband) for spatial positioning; USB – C 3.2 Gen 1; GPS/GLONASS/Beidou/Galileo/QZSS
Sensors	In – display fingerprint, accelerometer, gyro, proximity, compass, ambient light, laser AF sensor

Core Features & Technical Breakdown

1. Under – Display Camera (UDC/CUP) – The Flagship Innovation

The MIX 4’s UDC was a breakthrough in full – screen design, solving the long – standing trade – off between screen integrity and selfie functionality:

Customized Sub – Pixel Matrix: The 20MP front camera is hidden under a 5mm – diameter circular area on the top – center of the screen. Xiaomi used a diamond – like pixel arrangement with reduced pixel size (while maintaining density) to boost light transmission to the sensor without visible grid lines or color distortion.
Image Quality Optimization: It adopted AI – enhanced algorithms to compensate for light loss through the display, improving selfie clarity in both bright and low – light conditions (though low – light performance was slightly inferior to conventional punch – hole cameras at launch, later refined via MIUI updates).
True Full – Screen Experience: Unlike early UDC prototypes, the MIX 4’s display delivered uniform color and brightness across the entire panel, with no visible camera “shadow” under normal usage—realizing the MIX series’ original “bezel – less” vision.

2. Performance & Charging

Snapdragon 888+: The 5nm flagship chip delivered top – tier performance for 4K video editing, high – frame – rate gaming (e.g., Genshin Impact at medium – high settings), and multitasking. It also featured optimized thermal management to mitigate the Snapdragon 888 series’ heating issues.
120W HyperCharge: A standout feature, it could charge the 4500mAh battery from 0 to 100% in ~15 minutes—setting a benchmark for flagship fast charging in 2021. The 50W wireless charging and 10W reverse wireless further enhanced convenience for wireless – charging – enabled accessories.

3. Premium Design & Durability

Ceramic Back: The one – piece oxide zirconia ceramic back offered a unique, scratch – resistant finish with a premium luster, though it added to the 225g weight. Paired with the curved AMOLED and aluminum frame, it struck a balance between aesthetics and grip.
IP53 Rating: Basic dust and splash resistance for daily use, complemented by Gorilla Glass Victus on the front for drop protection.

4. Camera & Multimedia

Rear Triple – Camera: The 108MP wide sensor (OIS + Laser AF) ensured sharp, detailed photos in daylight; the 5x periscope telephoto enabled lossless zoom for distant subjects; the 123° ultrawide captured landscapes and group shots. Video capabilities included 8K@24fps and 4K@60fps recording.
Audio: Dual stereo speakers (tuned with Harman Kardon) and Dolby Atmos support for immersive multimedia and gaming audio; no 3.5mm headphone jack (replaced by USB – C and Bluetooth 5.2).

5. Software & Security

MIUI 12.5: Introduced features like Private Space, App Lock, and enhanced privacy controls, along with Xiaomi Knox multi – layered security to protect user data.
Long – term Updates: 3 years of OS upgrades (up to Android 14) and 4 years of security patches extended the device’s usable lifespan.

Market Reception & Legacy

The MIX 4 received mixed – to – positive reviews. Tech critics praised its groundbreaking UDC tech, 120W fast charging, and premium ceramic build, but noted minor trade – offs in UDC low – light selfie quality and the Snapdragon 888+’s occasional thermal throttling under heavy loads. It was a commercial success in China and select Asian markets, appealing to users tired of traditional screen cutouts.

Its legacy is twofold:

UDC Mainstream Catalyst: Proved that under – display cameras could be integrated into flagship devices at scale, paving the way for future Xiaomi flagships (e.g., 12S Ultra) and competitors to adopt UDC tech.
MIX Series Renaissance: Revived the MIX brand as a testbed for Xiaomi’s most innovative designs, moving beyond just “concept phones” to deliver practical, premium flagships with industry – leading features.