Kipsang won the 2012 and 2014 editions of the race through England's capital.
The Briton said he is not ready to race again after making his 26.2-mile debut in April.
The British distance runner owns the course record set in 2010.
Mo Farah placed eighth in his full marathon debut but vowed to run another one.
Vail's finish is the highest by an American in London since 2009.
The American said his run-up to London was the best training for a marathon he's had.
The two runners will take to the streets of London in Mo Farah’s shadow this weekend.
The double Olympic gold medalist finished second despite hitting the pavement hard.
The double Olympic gold medalist will have his hands full against a loaded field of superstars.