The official OTA to Android O for Pixel will likely drop in the first week or two of August. A bit earlier than Nexuses / Nougat last year.
— David Ruddock (@RDR0b11) June 6, 2017
While some details may be presumable, it’s not clear if the Pixel XL or applicable Nexus devices will get the update in the same timeframe or if full OTA and factory images will be available by then. The above information itself is subject to change.
Android O (perhaps Android 8.0) is currently in the second beta stage and should hit another intermediate stage in a week or so. One last preview stage is scheduled before August before final release sometime in the third quarter.
The first images for Android Nougat landed in the fourth week of August last year, beating out fall dates that followed Google Nexus hardware events years before. OEM updates will take a while longer after that point.