The Android O Developer Preview 3 is the latest preview version of Android O that will bring final APIs and official SDK. This update has not been made available OTA to devices enrolled into Android Beta program yet. But Google has made Android O Developer Preview 3 Factory images available on its developer website.
The Dev Preview 3 is termed as OPP3.170518.006. Factory images are available for Nexus 5X, Nexus 6P, Nexus Player, Pixel C, Pixel, and Pixel XL.
Download factory images by following the links below