https://www.cnet.com/news/will-my-iphone-xs-fit-in-a-iphone-x-case-yes/

Buying Apple's new iPhone XS may take a toll on your wallet, but you'll be able to save money on buying a phone case if you have an iPhone X case lying around.

That's because iPhone X cases fit on the iPhone XS. Both iPhones have the same height, width and depth, according to Apple's website.