The update, rolled out with the latest app update, allows you to open new incognito sessions directly from the app. As with Chrome, an incognito session in the Google app allows you to browse and search privately without your history being saved. You can turn on incognito in the app's settings or from your iPhone's home screen using 3D touch.
Just like in Chrome, the app will switch to a dark theme when you're in incognito mode to differentiate it from a normal browsing session. For extra security, you can also enable Touch ID so that others won't be able to access a prior incognito session without authenticating their identity.
It's a small feature but an important one, particularly for the privacy-conscious. While the Chrome app and Apple's Safari have incognito and private browsing, respectively, Google's app has the added benefit of Google Now cards (the service’s predictive search results based on your interests and habits), which may make it a more convenient choice.
Elsewhere, the app update also added the ability to view YouTube videos directly within search results, so you don't need to open a separate app or web page