Foster, 15, had a time of 1:57.87 which was a significant drop from his previous best time. The meet was for individuals aged 18-and-under.
“That is the fastest anyone has gone at that age -- ever,” Olympian Aaron Peirsol said on the USA Swimming Deck Pass show, according to the Manta Rays.
Foster earned one of 10 medals for Team USA Monday. The U.S. won 32 total medals including 12 gold to top the medal table in Indianapolis.
Foster had an excellent prelim swim in the 200 backstroke going 1:59.44 earlier on Monday.
Foster, a sophomore at St. Xavier High School, enjoyed the strong support from his Manta Rays teammates at the meet.
Foster competed in the Olympic Trials in the 400 individual medley in 2016.