T-Mobile CTO Neville Ray made a couple of announcements recently that detail where T-Mo has been making network improvements, and recentely Ray dropped another bit of good news.
Ray says that T-Mobile has added low-band LTE to hundreds of cell sites in two weeks.
T-Mobile has confirmed to me that this low-band LTE expansion is different than the one that Ray announced last week. One thing that is similar about this latest expansion, though, is that it includes a mix of 600MHz and 700MHz coverage.
Source: https://www.tmonews.com/2018/03/t-mobile-cto-low-band-lte-upgrades-rolled-out/