Almost all the smartphones can create hotspots to share internet connections, but this is often tricky and various problems occur while trying to make connection to other devices. Google fixed such problems and came with a feature that insures that the smartphones are always online. This new feature is called ‘Instant Tethering’.
This seems to be a feature available only to the android users having Google devices who connect their devices through a single Google account. So if you do have an Android tablet that loses internet, then this can be a very useful feature for you to stay online.
The basic idea is that if two Google devices are signed-in from the same Google account they will be able to connect to the internet if one is accessing mobile data. When multiple devices are connected using the same Google ID and one device loses a connection, the internet connection of other devices will be automatically offered.
This new feature is currently coming out as an update to Google Play Services. Its very limited for now due to a server-side restriction. Only devices like Pixel and Nexus will be able to use this feature which are running the latest Android 7.1.1, and they can also their internet connection with tablets like Nexus 9 and Pixel C and not the other way around. Pixel smartphones can share their internet with one another but Google is still testing this feature to understand how it works under different conditions.