Because Koech has admitted to cheating, the sentence is reduced by one year, the United States Anti-Doping Agency (Usada) said in a statement.
Koech was strongest in the 800 meters for a long time, but last season he broke through in the 1500 meters, including a Diamond League victory in Morocco. In the race he improved his personal best by six seconds.
He also became the American champion after beating Olympic gold medallist Cole Hocker in the final.
At the World Championships in Tokyo in September, Koech finished 13th.
He is now stripped of all results after July 30 last year.
Koech was born in Kenya but has competed for the United States since 2021.
