The Mi 8 comes with the latest version of Android, 8.1 Oreo. Being a Xiaomi phone, however, it's got a thoroughly customized proprietary layer of MIUI on top, version 9.5(.6.0, for those who are counting). MIUI 10 is right around the corner, but no OTA has shown up during the review process.
A new addition on the Mi 8 is the always on display, with a clock, date and notifications. You don't get anything in the way of settings for different styles - it is what it is. You do get the option to schedule when it turns on and off, or keep it on all the time.
There's an entire Full screen display menu where you get options for gesture navigation. Effectively, you can replace the navigation bar with a set of swipe actions - swipe up from the bottom for Home, swipe up and hold for the task switcher, and swipe in from either edge to go back. And if you think that last bit would interfere with apps that use the swipe in gesture to access a drawer menu, it doesn't - just swipe in a little higher and you'll get the drawer.
Inside the notch is Xiaomi's quasi Face ID system - an infrared illuminator and camera for facial recognition. Mind you, it's not the same as Apple's Face ID in that there's no 3D mapping going on here - the more exclusive Mi 8 Explorer does use a similar solution, but not this Mi 8. In any case, we found the face recognition to work super fast with only a minor difference in speed in dark environments. Additionally, it's somewhat more secure than some other implementations because it does require that you have at least one eye open to unlock the phone.
However, and Xiaomi warns you of it, the Mi 8's face recognition isn't as secure as fingerprint recognition, so it's a good thing then that the phone has that too. The sensor is on the back, enrollment is quick, and unlocking is near instant.
Unlocking the Mi 8 takes you to the homescreen, which is where all your apps are - MIUI emulates iOS in that respect by offering a single-tiered interface. The quick toggles and notification area have remained unchanged in MIUI for quite some time, unlike Google's own which get a redesign for every version. Recent apps look very much like the iOS app switcher, too. Apps are aligned next to each other and you flick them up to close them.
A swipe to the right reveals the App vault pane (also called Guide) with shortcuts to frequently used apps and a peek at Mi Notes and upcoming calendar events. According to MIUI forums, this page can only be disabled on the Chinese version of the ROM. Since ours is the Chinese version, a bunch of the default cards are rather... foreign to us.
The Security app is a hub that offers you options to scan your phone for malware, manage your blacklist, manage or restrict your data usage, configure battery behavior, and free up some RAM. It can also manage the permissions of your installed apps and allows you to define the battery behavior of selected apps and applies restrictions only to the apps you choose.
MIUI also offers proprietary Gallery, Music, and Video player. If you are running on a Chinese ROM, then the Music and Video app will also allow access to local (paid) streaming services. A ton of handy apps come pre-loaded too - voice/screen recorders, barcode/document scanner, compass/level, file manager, notes.
As for GPS accuracy, we grabbed the Mi 8 and a few phones we had lying around (Pixel 2 XL, Galaxy Note8, and Xperia XZ2 Compact) and headed out. While not entirely scientific, our head-to-head test gave us some insight, nonetheless.
First off, apparently the Mi 8 does tap into one extra band of certain satellites, and even though it doesn't really report which bands it uses, we're assuming it's the L5 in addition to the L1. The rest of the phones only reported connection of one band per satellite.
Looking at the plots from the GPS logging app we used on all of them (with the same settings, of course), we found that the Mi 8 was, indeed, able to more accurately track our movement. That appeared to be the case in both driving, and strolling through the park. It's hard to quantify just how much more accurate the Mi 8 was, and some extra testing sure is in order. In any case, we're liking where things are going.
If you want to build a flagship and you don't make your own chipsets (like Samsung and Huawei do), you're using the latest and greatest Qualcomm has to offer. That logic applies very much to the Mi 8 and it relies on the Snapdragon 845. All versions of the regular Mi 8 come with 6 gigs of RAM, and only the Explorer edition gets 8GB.
Xiaomi phones typically take top spots in benchmark charts - look at the Mi Mix 2S below. It appears that the Mi 8 is tuned differently, and the heating up we observed could be evidence of internal design limitations that wouldn't allow Xiaomi to squeeze out the absolute best of the Snapdragon.
Update, June 28:
Investigating further the low benchmark numbers we published initially, we re-ran all benchmarks while actively cooling the phone. It's only then that the Mi 8 was able to match the benchmark scores expected from the S845 chip. Without the help of the cooler, severe thermal throttling leads to what we would consider mere S835-level performance - it's not bad, but it's not stellar either. You will find the scores below along with the previous ones. We've also updated the texts that go along with the scores to take into account this new finding.
Starting with Geekbench, you will see that thermal management is not a big issue when a single core is involved. The extra cooling helped only in the multi-core test.
Higher is better
Higher is better
Where the Mi 8 wasn't posting proper Snapdragon 845 grade scores in Antutu before we applied some extra cooling. Without the extra help, the latest Xiaomi's scores in this compound benchmark are more in the Snapdragon 835 ballpark and about as much as the Kirin 970 (Huawei P20 Pro and Mate 10) pump out.
Higher is better
In graphics-specific benchmarks the Mi 8 is also ever so slightly behind its similarly equipped competitors. The lower resolution display (1080p vs. 1440p) gives it a slight edge over some rivals in the onscreen tests, but there is 1080p competition too and those do manage an extra frame per second. The extra cooling really helped achieve its best. We don't suggest that you have to cool your phone while gaming. This scenario just serves to show the toll the thermal management takes on the device performance.
Higher is better
In the on-screen test, however, the extra cooling didn't help the phone score higher but that's fine because its score was not far back behind the SD845-level, to begin with. And since this is the test most relevant to day-to-day gaming performance, we'd reckon that Xiaomi has done a nice job of providing consistent performance under load - even if not the chart-topping.
Higher is better
Overall, the Mi 8 is a strong performer. Unfortunately, it fails to deliver the benchmark results we've come to expect from the chip inside it (due to bad thermal management as it turned out). It's plenty powerful but just not SD845-level powerful. In any case, bear in mind that a lot of other phones with top-tier chipsets throttle when put under load for longer. But they were at least capable of producing the top scores mentioned we quote above while the Mi 8 never did - at least not without the help of some active cooling applied to its back.