The rivals have been competing against each other since 2006.
One of them is Elise Cranny, a 4:15 miler.
He helped Team USA bring home the gold at the World 24-hour Championships.
Zoe Romano was the first woman to run across the U.S. without assistance in 2011.
Those who failed to finish due to bombings offered guaranteed entry for next year.
She's making her debut there.
The Ethiopians aren't competing against each other.
The Ethiopian champion says patience is key.
Twenty pairs are donated to homeless shelters in Boston.
It will be the American marathoner's second race of the 2013 season.