If you recall, the iPhone X is IP67 rated for water/dust resistance, while the iPhone XS family bumps that up to IP68. As a result, the seals holding the display into place are stronger, making removing it more of a hassle (although not impossible).
The other thing of note is that the L-shaped battery from last year remains. However, while there were two separate cells on the iPhone X, the battery in the iPhone XS appears to be a large, single unit. Speaking of the battery, capacity has actually dropped slightly compared to last year (2,658 mAh versus 2,716 mAh). Despite the decrease in capacity, efficiencies made possible by the 7nm A12 Bionic SoC mean that the iPhone XS actually boasts 30 mins of additional runtime compared to its predecessor.
This confirms filings from China's Ministry of Industry and Information Technology (TENAA), which first revealed yesterday that the iPhone XS has a 2,658 mAh battery. Although the iPhone XS Max hasn't yet gone under the knife, its TENAA filing suggests that it will have a 3,174 mAh battery -- the largest ever installed in an iPhone. However, even that pales in comparison to the Galaxy Note 9, which packs in a massive 4,000 mAh lithium-ion battery. The iPhone XR reportedly has a 2,942 mAh battery.
Other details gleaned from the TENNA filings show that both the iPhone XS and iPhone XS include 4GB of RAM, while the entry-level iPhone XR has just 3GB of RAM (the same about found on the iPhone X and iPhone 8 Plus).