The System UI Tuner has never really been a feature for the masses. It was a way of hiding experimental features from the majority of users — you had to long press the quick settings cog to activate it — while still letting the more inquisitive of us play around if we wished. In the early Oreo developer previews there were quite a few interesting things in there, but by DP3 it was reduced to just a couple of status bar and DND settings. In Android P, it appears to have been removed entirely.

Some of the features previously found in the System UI Tuner settings have graduated into Android proper, such as demo mode (now referred to as 'System UI demo mode' in developer options), battery percentage in the status bar, and picture-in-picture mode. Others, including additional navigation bar buttons and customizable lockscreen shortcuts, didn't quite make the grade.

This is just the first developer preview of Android P, so we can't be sure Google won't reinstate a System UI Tuner of some kind in future releases. That's what the previews are for, after all, and we can expect tons of further additions and removals down the line. Let's hope there are some exciting new features in the works that simply aren't ready to be sampled yet.

Alternatively, it's possible that it still exists but its method of activation has been changed. If any of you have stumbled upon it, do let us know.

UPDATE: 2018/03/29 12:42pm PDT BY

Turns out this is still around, just no longer in any user-facing form. We'll see if it returns in full or departs in subsequent previews.

Thanks: Nick Cipriani