Oatmeal Cookie could be the official name for Android 8.0 according to some recently discovered references in the source code. According to the details of the source code there are references to something called oc-dev being tested on Sailfish. Sailfish is the Google Pixel (Marlin is the Pixel XL) and it's reported that oc-dev follows along the same lines of the way Google makes references to the operating system versions within the source code. While these details don't actually list the name as Oatmeal Cookie, the letters "o" and "c" seem to suggest the two parts of the name for Android 8.0, and that it likely will be Oatmeal Cookie when it is finally pushed out by Google later this year to its crop of compatible smartphones and other devices.
This in particular isn't a whole lot to go off of but something being referred as oc and it being tested on the Pixel makes for a pretty compelling case that Oatmeal Cookie is likely to be Google's final name choice for the upcoming version of the Android software. In addition to the oc-dev reference recently found in the source code, it's also been pointed out that a few different people have noted on Twitter that they spotted Oatmeal Cookie being referenced in some of the sessions that were happening at Google I/O back in may.
These references which actually list "oatmeal cookie" along with the oc-dev reference seem to be all but giving the name away, though nothing is truly confirmed just yet and the public won't actually know for sure what Android 8.0 will be called until Google officially announces it later this year. Google did at least confirm that Android O will be 8.0 though. As it stands Android O is in its third developer preview phase and it was expected that there would be four developer previews before Google sent out the final version of Android 8.0 to its list of supported devices which of course includes the Google Pixel and Google Pixel XL. Oreo has long been the favorite and most suspected to be the official Android O name, but perhaps these references to oatmeal cookie shed some light on the topic.