It's been nearly a year since AT&T and Verizon reintroduced their unlimited plans, inviting their customers to download, stream and surf at their whim. But those unlimited plans came with a performance price. 4G speeds for both operators began dropping steadily in OpenSignal's tests soon after the new plans debuted in February, and in our August State of Mobile Networks report we found that Verizon's average LTE download had fallen 2 Mbps in six months, while AT&T's average was down by a megabit.
A half year later, there's both good news and bad news for AT&T and Verizon. The good news is Ma Bell and Big Red seem to have stanched the bleeding created by unlimited plans. After six straight months of tracking decreases in LTE speeds, in September speeds for both operators leveled out in our measurements, and in Verizon's case, speeds started creeping back upward. The bad news is in November, both AT&T and Verizon were still well short of their 4G speed highs established in February. Meanwhile, Sprint and T-Mobile speeds have steadily increased over the same 11-month period. T-Mobile was nearly 3 Mbps ahead of Verizon in our 4G speed metric in November, locking down its lead in the LTE speed race, while Sprint had closed much of the speed gap between itself and AT&T.
In the chart above, we've plotted the history of all four operators' 4G speed metrics in 11 three-month test periods in 2017. The first test period covered November 2016 to January of 2017, while the last covered September through November. As you can see, both Verizon and AT&T's highest speed scores for the year came in the Dec-Feb test window, right before the new unlimited plans became public. Over the next six months, both operators' average speed scores dropped considerably, and both hit lows in August: 12.1 Mbps for AT&T and 14.4 Mbps for Verizon. But starting in the July-Sept test period, those declines stopped. Our results show AT&T's speeds remained relatively steady for the next few months, but Verizon's speeds began to climb back up as we rolled into the third quarter. By the end of November, Verizon's average 4G speed had increased 1.5 Mbps in just three months in our measurements.
However, Sprint and T-Mobile seem to have taken advantage of AT&T and Verizon's period of decline. Sprint's speeds have been both up and down in the last year, but it ended November on a new high. Its tested average 4G download of 11.8 Mbps is more than 2 Mbps faster than its February result. Meanwhile, T-Mobile really took advantage of the situation to solidify its position on the top of our 4G speed chart. T-Mobile posted steady gains in 4G speed in our measurements in nearly every month of 2017. At the beginning of last year, T-Mobile and Verizon were deadlocked for our 4G speed award. By November T-Mobile had established itself as the clear leader in our 4G speed metric.
It looks like both AT&T and Verizon have figured out how to keep the data deluge from unlimited plans in check. The question now is if they can fully recover, bringing their average speeds back to pre-unlimited plan levels. Verizon appears to be well on its way. If Big Red's speeds continue to increase at the rate they have in the last few months, it will be back to its February high of 17.6 Mbps in no time. AT&T has a little more work to do to fully reverse its speed decline. But even if both operators fully recover, they will likely find that the unlimited crisis has cost them major stakes in the 4G race. T-Mobile has bounded ahead of all its competitors in speed, and Sprint -- which is always placed dead last in our 4G speed metric -- has gained considerable ground.
Stay tuned. OpenSignal will look at the 3G and 4G metrics for all four major U.S. operators in its upcoming State of Mobile Network: USA report. We'll also delve further into the impact of unlimited plans on mobile data speeds over the last year and the reasons behind AT&T and Verizon's recovery.