The USA international goalkeeper made 21 appearances in all competitions after joining the Club in the summer of 2019.
During his spell at the Etihad Stadium, Steffen was part of two Premier League title-winning squads, featuring in every competition for City.
He also helped Pep Guardiola’s men lift the Carabao Cup in 2021, keeping a clean sheet in the final against Tottenham Hotspur as City ran out 1-0 winners.
The 28-year-old then spent the entirety of the 2022/23 campaign on loan at Middlesbrough, turning out 45 times as they reached the Championship play-offs.
And Steffen will now return to the United States for the latest chapter of his career, moving to Colorado on a permanent deal.
Everyone at Manchester City would like to thank Zack for his effort and wish him the best of the luck in the future.