https://www.techradar.com/news/google-pixel-3-and-pixel-3-xl-cameras-detailed-in-latest-leak

We’ve known for a while that both the Pixel 3 and Pixel 3 XL will probably have dual front-facing cameras, but now we have a good idea of what that extra lens is for.

According to sources speaking to 9to5Google, one of the lenses will be wide-angle, and the two combined will allow for better bokeh effects (the blurring of a background in a shot, often known as portrait mode).