http://www.techradar.com/news/no-dual-sim-capabilities-on-google-pixel-2

The Google Pixel 2 and the Pixel 2 XL are the first phones that are equipped with an eSIM. The eSIM is the next step in the evolution of SIM cards and instead of using a physical SIM card, it lets you change your network provider using software. 

The technology isn't new - we've already seen Apple's version of it as well as other products such as Samsung's Gear S3 smartwatch use it but it is the first time it's been equipped on a phone.