The menu button used to be oh-so-important to Android in the early years. Google ditched it pretty early on with the introduction of the Galaxy Nexus, but Samsung's flagship Galaxy Note III was released in late 2013 and still had one on board.
But even after menu buttons lost their permanent spots on the chins of phones, some still persisted through long-presses of the multitasking button. You could even find cheaper devices with dedicated menu buttons to the right of their multitasking buttons, and if you really wanted one on your current phone, some custom ROMs would allow you to add one there. In 2017, however, we thought menu buttons were long gone. Google apparently had other ideas with the brand-new Pixel 2.
Ryan discovered this on his Pixel 2 XL review unit through purely accidental means, and David found that his had the same "feature." Those of us on the AP team who still have the original Pixels on Oreo tried furiously tapping in the same area on other phones to no avail. Just another case of Google keeping all the best features for its newest devices, I guess. Do they even care about those who don't have the money to buy the new Google phone every year?
But on a serious note, when exactly does this invisible menu button function? We know that it works in settings from the video above, but from a quick scan of apps, that seems to be one of the only ones to support it. In Google Maps, the button vibrates, but nothing else happens. But in Inbox and Google Photos, it does nothing. Currently, the only way to trigger a menu button to appear there on a stock device (without any nav bar customization apps, built-in or otherwise) is by using an app with a build target of API 13 (3.2 Honeycomb) or lower.
The best explanation we can come up with is that this was simply left there in development. Whatever the true reasoning behind this mysterious button is, those of you future Pixel 2 owners out there can rest in peace knowing that your phone will have a feature that only antique Android devices share. Pixel 2 phones began shipping out today and will be delivered as early as tomorrow, so make sure to tap repeatedly on the bottom right of your screen when you get yours.
Alternative title (by Ryne): Secret recordings, secret menus: What Google keeps from us