Adaptive brightness is not present in notification bar and altogether does not work My Nexus 7 2013 has updated with OTA update to Android 5.0.1. 

The notification bar has changed. Now when I change brightness, there is no button for auto-adjustment. It currently looks like this:



In settings, I can find Adaptive brightness settings - optimize brightness level for available light. However this does not work as expected. It just seems I have two different brightness settings. If I turn it on and set manually via notification bar to maximum, it is maximum, although the settings is ON. Then I turn it off and set it to maximum and it lets me do it too. When it is turned on, the brightness is just slightly darker than the turned OFF mode. However, it is always exactly as I set it with this small offset. It does not correspond to the external light. 

It seems like it is a bug, but I can't tell. Do you experience the same with your Nexus 7 2013? Is the "auto" button missing in all lollipops? Does it mean that when you want to go to auto-brightness mode you have to enter settings and brightness via more like 5 clicks? (two swipe downs, settings, brightness, turn on)
Android has removed &quot;Auto-brightness&quot; in place of &quot;Adaptive brightness&quot; on Android 5.0 Lollipop.
From Android Police,

If you're looking for the auto-brightness switch on the Android L preview build, you won't find it. That's because it's been replaced with the adaptive brightness toggle. [...]
In short, adaptive brightness is like quasi-autobrightness. You're essentially setting a &quot;range&quot; of available brightness levels when this feature is turned on, so that if you have display brightness set to 50%, the phone may only actually adjust itself between 40 and 70% brightness in a given situation. This is as opposed to completely automatic brightness, which typically gives you the full spectrum of brightness adjustments depending on the ambient light. The problem with fully automatic brightness is that's it's often slow and a poor judge of what level of brightness your eyes really need. So, this adaptive mode allows you to set a baseline brightness that the phone will then adjust from based on your surroundings.

If adaptive brightness is active, it will be always active even if the brightness is changed from the quick setting panel, because it will only change the baseline brightness.
On the other hand, it's correct that there is no quick setting to toggle &quot;Adaptive brightness&quot; on stock ROM. It seems the only way to do that is with 3rd-party apps, but I didn't found any as of current writing.