New "Instant Tethering" feature rolling out to select Android devices
Select Pixel and Nexus devices are now able to use the new "Instant Tethering" feature. The Pixel, Pixel XL, Pixel C, Nexus 6, Nexus 5X, and Nexus 6P are all capable of automatically using a shared connection with Android 6.0 and up, while all those (minus the Pixel C) will be able to host connections automatically once running Android 7.1.1 and up.
Instant Tethering is different from the existing tethering (hotspot) feature in that it automates the connection process. With the existing feature, the host device must turn the hotspot on manually. Then the client device can connect to the host through an ad-hoc WiFi network. After an initial pairing process similar to a Bluetooth device, Instant Tethering will automatically detect if a client device is nearby without an internet connection. If the device has no connection, the host will automatically share internet with paired clients. To save battery, the host will automatically stop Tethering after 10 minutes of inactivity.
The mode can be turned on by going to the Settings app then selecting "Google" then "Instant Tethering". As tethering can use a lot of battery, Google recommends keeping the host device plugged in if possible.