Here is how to perform a factory reset on Google Pixel under Android 8 Oreo. The steps differ from the earlier tutorials because of changes in Android 8.0.
Google Pixel devices receive the first update for new Android 8.0.0 Oreo. The update weight is 42 mb. It contains the security patch level for September 5, 2017 and brings stability improvements and bug fixes. I see OPR3.170623.007 on my Google Pixel US Version (G-2PW4100).