Union Pacific 4023 is a preserved member of the 4-8-8-4 Big Boy class built by the American Locomotive Company in Schenectady, New York in November 1944. It is one of eight surviving UP Big Boys being preserved across the United States. 4023 also has the distinction of being the only surviving Big Boy that was part of the second group built in 1944, as all the other surviving Big Boys are from the first group built in 1941.