Ben Schoon, 9to5Google:

Almost every Android smartphone ships with an oleophobic coating on the glass, and the purpose of that is to help make fingerprints easier to get off of the display. In short, it keeps the oil from your fingertips from adhering to the glass, and it also makes water easier to wipe away.

Over time, this coating wears off, but it usually takes at least a few months or years of intense usage. On the Pixel 2 XL, however, some owners are having this come up within just a couple of weeks.

iPhones have shipped with an oleophobic coating, starting with the iPhone 3GS. This is mature technology. Surprising to see this issue crop up with the Pixel 2.

I’ve got an email in to Google PR asking about this issue, will update this post if and when I get a reply.