Google just posted the Android security update for September 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 (OPR1.170623.026, OPR3.170623.007), Pixel C (OPR1.170623.026), Nexus 6P (OPR6.170623.017), and Nexus 5X (OPR4.170623.006).
We’ve also got new 7.1.1 files for Nexus 6 (NGI55D) and Nexus 9 (N9F27L, N4F27O).
The notes here for each Pixel update indicate that OPR1.170623.026 is for Project Fi and Canada models, while OPR3.170623.007 must be for everyone else.
As more files arrive, we’ll update this post.
UPDATE: Nexus Player Oreo files are now up.