5-6hrs seems to be the averageHaven't had the need to charge it before the end of day yet.
I too am getting 6 hours + of heavy usage (lots of YouTube, music streaming, etc) on my Pixel 2 XL but see the real possibility of significantly more usage time if Google is able to integrate successfully the haptic technology mentioned previously from their recent acquisition of the Cambridge-based Redux ST.
This link provides a hands-on experience with Redux's technology and its potential for multiple use cases on future Pixels, Chromebooks, self driving vehicles, etc.
http://www.businessinsider.com/haptic-feedback-technology-redux-st-google-acquired-2018-1