Android 8.1 has quite a few minor changes, ranging from a new easter egg to the new dimming navigation bar. Another small tweak is the icon for Android System notifications, which are used to display messages about updates, debugging, and other similar functions.

The icon used in 8.0 is the same used in the developer previews - three circles. Since the Oreo name wasn't confirmed until very close to release, it makes sense that the Oreo branding wouldn't be present at that time. Now the icon has been tweaked in Android 8.1, turning it into an Oreo cookie.

There's not much else to say about the change. It wasn't an Oreo before, and now it is.