The U.S. economy expanded at a 4.2 percent annual rate in April, May and June.
The second-quarter growth figure is one-tenth of a percent higher than initial estimates.
"The economy is in good shape," according to PNC Bank Chief Economist Gus Faucher. He writes that this is the best "year-over-year increase in three years."
But Faucher also says growth above four percent is "unsustainable" and the economy is "set to slow somewhat in the second half of 2018," and hit 3.4 percent for the whole year. He predicts U.S. economic growth will slow further in 2019 and 2020 as the "stimulus from tax cuts and spending increases fades."
Wednesday's report from the Commerce Department is a routine revision made as more complete data becomes available.
Growth figures were boosted by a decline in imports, particularly petroleum, and by some temporary factors.
One of those factors is a surge in soybean exports, which were rushed at a faster-than-usual pace to beat tariffs imposed by China in retaliation for new tariffs imposed by the Trump administration on Chinese goods.
The new second-quarter figures are nearly double the performance in January, February and March.