Google just posted the Android security update for October 2017 and the files are already live for a number of devices, both Pixel and Nexus.
So far, we are seeing 8.0.0 files for Pixel and Pixel XL (OPR1.170623.027, OPR3.170623.008), Pixel C (OPR1.170623.027), Nexus 6P (OPR5.170623.007), and Nexus 5X (OPR4.170623.009). We have nothing yet for the Nexus Player.
Others receiving updates are the Nexus 6 (Android 7.1.1 – N6F27M, NGI77B) and Nexus 9 (Android 7.1.1 – N4F27P, N9F27M).
As for notes, Google says that Pixel/XL build OPR1.170623.027 is for Project Fi and Canada, so the other build (OPR3.170623.008) should be for everyone else. The Nexus 6 build NGI77B is for Verizon customers, so N6F27M should be the general update for all others.
You can grab each image or OTA file at the links below. For instructions on how to flash a factory image, here you go. For instructions on how to flash an OTA .zip file, here you go.
As more files arrive, we’ll update this post.