Android Oreo 8.0 has already hit the Google Pixel and Google Pixel XL. Now its for Nexus(Nexus 5X and Nexus 6P) device will start to see the major Android update which is priority for Oreo as per the Google.
Canadian carrier Rogers has its firmware schedule up and it shows that the Nexus 6P is expected to receive Android 8.0 Oreo on September 11. Here this list may be not accurate one. We can expect the Oreo update before or after september 11.