https://www.theverge.com/2017/9/19/16334690/t-mobile-unlimited-data-cap-increase-32gb-50gb-deprioritization

T-Mobile just announced that it’s increasing its soft cap for unlimited data plans from 32GB to 50GB, a move that continues to put it far ahead of competitors. In comparison, Verizon and AT&T have 22GB caps, while Sprint’s is 23GB.

If you’re new to modern unlimited data plans, you may be wondering why a plan that purports to be “unlimited” would still have a data cap at all. The answer is that, while technically data is unlimited, carriers include soft caps. Once you’ve used up your quota, your data is de-prioritized to slower speeds if the network is in high demand.