The LTE on your phone is pretty fast these days as long as you've got a good signal. It's not as fast as LTE on the Galaxy S8, though. T-Mobile has posted a demo of the GS8 hitting nearly 1Gbps in a laboratory test. It won't do this in real life, but the hardware can do it. T-mobile is working to upgrade its network to take full advantage.
The GS8 is powered by the Snapdragon 835, which has Qualcomm's latest X16 LTE modem. That means it's capable of gigabit speeds, but that depends on network support and backhaul as well. T-Mobile's national network doesn't support gigabit LTE just yet, so this test was conducted in the carrier's Bellevue lab.
Gigabit LTE requires the use of three different technologies—carrier aggregation, 4x4 MIMO, and 256-QAM. The Galaxy S8 supports all of them, and T-Mobile says that's a first. This point is a little vague because the Galaxy S7 supported these technologies, as far as we know. Maybe it means the GS8 is the first to do this on all T-Mobile's bands? T-Mobile does confirm that the Galaxy S8 will be the first to support LTE-U, which taps into unlicensed spectrum up to 5GHz to increase speeds. Likewise, the GS8 supports T-Mobile's new AWS-3 bands for more capacity.
T-Mobile plans to continue rolling out support for 4x4 MIMO and carrier aggregation in more markets throughout 2017. With that tech, the carrier claims the GS8 could double LTE speeds for users in nearly 300 cities nationwide. The pieces could be in place for gigabit LTE later this year. Will it actually be that fast? I guess we'll have to wait and see.