As Neowin originally reported in September, Microsoft released the Surface Pro with Advanced LTE on December 1. Unfortunately for consumers, it's only available for business customers, while everyone else will be able to grab it in 2018.
While it was originally only available from retail partners, the Commercial Surface Pro with LTE popped up on the Microsoft Store website in various regions, although it shows as out of stock. Today though, various physical stores are showing as having it available to purchase.
It's nothing new for Microsoft to have a separate 'Commercial' listing for its Surface devices, so it's no surprise that that's where the Pro with LTE appeared first. You'll also find storage and RAM configurations that aren't available to consumers, such as a Pro with a Core i5, 16GB RAM, and 256GB storage, and a Laptop with a Core i5, 8GB RAM, and 128GB storage.
It's unclear what the restrictions are for actually buying one though, or if the user experience is different on the Commercial model. You can find which stores have them by going to the Microsoft Store listing and clicking 'Find in store'. The one with 4GB RAM and 128GB storage is $1,149, and the one with 8GB RAM and 256GB storage is $1,449.
Both of them are only available with a Core i5 processor, which is because the Qualcomm Snapdragon X16 modem is placed where the fan is located on the Core i7 model. While the modem supports gigabit LTE speeds, the device is capped at 450Mbps, although that could change in a future firmware update.