If you were wondering whether a Google Pixel 4 is in development, the first official references to the phone have been uncovered.
The Google Pixel 3 is not even six months old, and yet 9to5Google noticed a few mentions of Google’s next Pixel, the Google Pixel 4, by a Google employee who posted to an Android Open Source Project code change. Google’s own software engineer made three distinct references to the yet-to-be-announced device, while discussing a fix for an issue with Google's memory error detection tool (KASAN).
There's little information to glean from the post, but it suggests that Google Pixel 4 units could be in testing. It seems Google wants to begin testing a bug fix on Google Pixel 3 units before then testing on, presumably, pre-production Pixel 4 units. Pixel 4 likely won't be unveiled until October, so with such a long time to go, rumours and leaks aren't exactly common. Pixel 4 is all but unknown to us.
There's speculation it could keep Google’s two-tone design, maybe add a second camera with a wide-angle lens, and ditch the notch. We've yet to see any concrete evidence, however, so much of this could change in the coming months.