Android 8.1 shows a persistent "apps consuming battery" alert in the notification shade. This is not entirely new, as Android 8.0 Oreo already introduced this alert, albeit with different wording. While the alert itself was introduced with 8.0, instead of apps consuming battery it was listed as apps running in background. You were able to tap on the alert if desired and find out which apps were running in the background if there were more than a few and not all could be listed. With Android 8.1, apps consuming battery is the new wording as mentioned above, and you can long press the alert just like before, but doing so gives a new option which wasn't previously available - the ability to disable the alert entirely.
This is likely a big thing for many users as a common complaint with Android 8.0 Oreo was the fact that this alert was even implemented in the first place. Granted, it probably wasn't viewed as annoying to all users and some probably found it to be rather useful, but there seemed to have been a number of users who saw it as pointless. Google obviously doesn't agree as it's kept the alert moving forward with the latest software, but it has changed things up by giving users the option to disable the alert if they don't want to see it, and without having to install an app from the Play Store to do so.
If you see the alert show up on your device with Android 8.1, then long press the alert, you should see something like in the second screenshot below, with a toggle switch that you can tap to disable the alert. While this alert doesn't need to be there, it does stick with the theme of keeping things as convenient as possible, since you won't have to go all the way to settings, tap on the battery section and from there view which apps are using up your phone's battery life. Seeing it in a alert is much simpler and since it's right in the notification shade you have next to no steps to get this information, and if for whatever reason you decide you no longer want the alert to show up, the next time it appears you can utilize the disable toggle.