The newborn was born at 1:21 a.m. on Wednesday and weighed 8 pounds, 15 oz., according to the website.
Kunis' rep previously confirmed the birth to ABC News.
Baby Dimitri is the second child for the couple. Their eldest, daughter Wyatt, is 2.
Kutcher, 38, and Kunis, 33, were first linked in 2012 and married in 2015. Though both have chosen careers in Hollywood, Kutcher told A Plus that he hopes for privacy for their kids.
"We'd like to allow our kids to make their own choices on whether to have a life in the public eye or not," he said. "We don't want to make the choice for them."