Android 8.0 Oreo debuted over a week ago but many Nexus and Pixel devices are still waiting for the official OTA update. Luckily, Google has published the OTA update files for all supported Nexus and Pixel devices on its developer website. These files are accompanied by the updated Oreo factory images.
OTA update files allow you to manually update your Nexus or Pixel device. This has the same effect of flashing the factory images, but without the need of wiping the device and losing all existing data.
This is the first time, Google itself has posted the OTA update images. Traditionally someone would extract the OTA update URLs and share them online but getting these directly from Google makes things way easier.
You will still need a basic knowledge of using ADB to flash these on your Nexus or Pixel device. If you need a refresher, Google has also given basic instructions on its website.