https://www.theverge.com/2017/12/5/16739518/apple-iphone-x-unlocked-sim-free-available-now

Today, Apple started selling an unlocked, SIM-free model of the iPhone X through its website, Apple Store app, and retail locations. The unlocked version of the handset, which starts at $999, was previously only available if you bought it through Verizon or Best Buy, which charged a $100 premium over financed carrier versions of the phone until consumer backlash pushed the retailer to pull the product entirely.

Now, if you find the iPhone X on Apple’s website, you’ll have the option to buy either a GSM or CDMA version of the phone that works with either AT&T and T-Mobile or Verizon and Sprint. The new option, listed under SIM-free, let’s you purchase the iPhone X unlocked, meaning you can freely bring it to any carrier or use it with a prepaid SIM card.