A strong second leg from Michael Cherry put the U.S. into a clear lead, before Rai Benjamin held off Jamaica on the final lap for the win in 2 minutes 56.69 seconds. The bronze went to Belgium. Britain failed to finish after falling at a changeover.
The United States finished the championships top of the medal table with 14 gold medals, 11 silver and four bronze for a total 29. Kenya was second on gold medals with five, while Jamaica had the second-best total with 12.
The U.S. will host the next championships in Eugene, Oregon, in 2021.
The United States has dominated the women's 4x400-meter relay by using two hurdlers in the final.
The U.S. took the lead on the opening leg with Phyllis Francis, stretched the advantage with hurdlers Sydney McLaughlin and Dalilah Muhammad, before Wadeline Jonathas brought the win home in 3 minutes 18.92 seconds.
Poland snatched silver when Jamaica's Shericka Jackson faded on the final straight and dropped to bronze.
Allyson Felix didn't run for the U.S. in the final, but receives her record 13th world championship gold because she competed in the heats. Earlier this week, Muhammad set the world record in the 400-meter hurdles, just barely beating McLaughlin.
Minutes earlier, Anderson Peters won the men's javelin for Grenada with a throw of 86.89 meters after his closest rival Magnus Kirt withdrew injured.
That caps a breakout season for Peters, who won his second NCAA title for Mississippi State and gold at the Pan-American Games.
Kirt fell on his elbow during his fifth throw and was stretchered off with ice on his shoulder. However, his throw of 86.21 was still enough for silver ahead of third-place German Johannes Vetter.
Nia Ali has won the women's 100-meter hurdles for the United States, the Olympic silver medalist's first time on the podium at the world championships.
Ali took the lead early and held on to win in 12.34 seconds. Fellow American Kendra Harrison chased down the 2015 champion Danielle Williams for the silver in 12.46, one-hundredth of a second faster than the Jamaican.
"I'm so ecstatic right now," Ali said. "I'm truly at a loss for words."
Jamaica's Megan Tapper failed to finish after pulling up halfway with an apparent injury.
Malaika Mihambo of Germany has added the world long jump title to her European gold medal with one of the biggest leaps of recent years.
Mihambo jumped 7.30 meters in the third round, when she was facing elimination if she didn't improve her result. It was the second-best leap by anyone in the last 15 years, beaten only by a 7.31 from Brittney Reese of the United States in 2016.
No one else could come close Sunday.
The silver went to Ukraine's Maryna Bekh-Romanchuk with 6.92, one centimeter ahead of Nigerian bronze medalist Ese Brume.
Joshua Cheptegei has won the 10,000 meters gold for Uganda after a sprint finish.
Cheptegei and Ethiopia's Yomif Kejelcha were even all the way around the final lap until 2017 silver medalist Cheptegei produced a burst of pace on the final stretch to win.
His time of 26 minutes 48.36 seconds was the second-fastest at a world championships.
Rhonex Kipruto took the bronze for Kenya.
Allyson Felix can win a record 13th career world championship gold medal, but she won't be on the track.
Felix raced in the 4x400-meter relay heats for the United States but the whole team has been changed for the final.
The gold and silver medalists from the 400 hurdles, Dalilah Muhammad and Sydney McLaughlin, team up with Phyllis Francis and Wadeline Jonathas.
They replace Felix, Jessica Beard, Kendall Ellis and Courtney Okolo. Anyone who runs in a relay heat or final is eligible for a medal.
Timothy Cheruiyot has won the 1,500-meter gold after a daring breakaway from the pack.
Cheruiyot and fellow Kenyan Ronald Kwemoi led the race from the very start and Cheruiyot broke away on his own when Kwemoi started to fall back into the pack.
The 2012 Olympic champion Taoufik Makhloufi took the silver for Algeria after winning a hectic pack sprint on the last stretch, with bronze for Poland's Marcin Lewandowski.
It was the first gold medal at a major championships for Cheruiyot, who won world silver in 2017 and also has two silver medals from the African championships.
Kenya now has five gold medals from the championships, second only to the United States.
Danielle Williams of Jamaica is closing in on her second career world title after qualifying fastest in the women's 100-meter hurdles semifinals.
The 2015 gold medalist ran 12.41 seconds to win her semifinal in a close finish ahead of 2016 Olympic silver medalist Nia Ali of the United States.
Nigeria's Tobi Amusan and world indoor champion Kendra Harrison of the U.S. won the other two semifinals.
Those eliminated include the 2015 world silver medalist Cindy Roleder of Germany and the reigning European champion Elvira Herman of Belarus.
The United States is aiming to finish strongly as the women's 100-meter hurdles caps the final day of competition at the track and field world championships.
Kendra Harrison and Nia Ali lead the U.S. charge in the hurdles, with Jamaica's Danielle Williams also among the favorites.
Olympic champion Matthew Centrowitz of the U.S. is challenging in the 1,500 meters, though the final is likely to be much faster than the race he won in 2016 in Rio de Janeiro.
Men's and women's 4x400 relays end the championships, with Allyson Felix able to win a record 13th career gold medal at the world championships.
Germany's Malaika Mihambo is the favorite for women's long jump gold after coming top in qualifying, while medals are also on offer in the men's 10,000 meters and javelin.
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