Apple's latest flagship phone is a fancy new device with a gorgeous new screen - one that's so different, you'll need to make sure your existing apps, or apps you'll make soon, take this into account, regardless of whether it's an iOS or Android app.
Firstly, it's taller than what we've been accustomed to for the last few years; it's the same width as the last 3 generations of iPhone, but almost a fifth taller.
Also, the iconic home button is gone, replaced with a swipe-from-the-bottom-edge gesture.
Not to mention, the screen isn't a rectangle.
All of these present interesting new challenges (and opportunities) when it comes to UI/UX, so check out Apple's human interface guidelines (linked below) for their take on how you might want to adjust your apps to the iPhone X.
But also don't assume this is an iOS-only challenge. Flagship phones in general have been trending to taller aspect ratios, trying out non-standard screen shapes, and using edge swiping gestures even before the iPhone X, most notably, Samsung's efforts with their Edge and Infinity displays, leading to similar considerations that need to be made when developing for these devices.
But, I do have to stress, we should refer to designing and developing for this new generation of screens as a challenge - whilst in some ways a nuisance, it's more importantly, a positive opportunity to add value to our apps' user interfaces.
When designing for iPhone X, you must ensure that layouts fill the screen and aren't obscured by the device's rounded corners, sensor housing, or the indicator for accessing the Home screen.