The following update will be listed as “System Firmware Update – 9/18/2015” when you view your update history.
Surface Modem Firmware Update (v126.96.36.199) improves mobile broadband network stability (for Surface 3 (AT&T 4G LTE) and Surface 3 (4G LTE) in North America (non-AT&T)).
Surface Modem Firmware Update (v1521.04.10.0) improves mobile broadband network stability (for Surface 3 (Y!mobile 4G LTE) and Surface 3 (4G LTE) in Europe.
Before you go ahead with the update Microsoft warns:
Firmware updates cannot be uninstalled or reverted to an earlier version.
If you are a Surface 3 owner and you have not yet received the update Microsoft advises:
When Surface updates are provided via the Windows Update service, they are delivered in stages to Surface customers. As a result, not every Surface will receive the update at the same time, but the update will be delivered to all devices. If you have not received the update then please manually check Windows Update later.
If you are a Surface 3 owner who uses mobile broadband then this update will be essential for the stability of your connection.