Google will be shipping the Pixel and Pixel XL in a few weeks, but you can download the system dumps from the phones right now. Developer and occasional leaker LlabTooFeR has posted the files online, but don't get excited thinking these dumps will let you install Android 7.1 on your device. This is still a chance to get a look at the Pixel's software a little early, though.
The downloads contain three image files; one for boot, one for the system, and one called system_other with ODEX files. The images are (of course) based on Android 7.1. They have build number NDE63H and the security patch level for October 5th. The files are hosted on MEGA and are about 1.3GB total for each phone.
There are some updated APKs in the system image that we're going through, and in some cases adding to APK Mirror. If you want to take a closer look at the system dumps and try to tease out their secrets, go right ahead. You'll probably find wallpapers, boot animations, and other odds and ends. It's the best we've got until the phones arrive.