The Bengals also promoted S Brandon Wilson and DT Josh Tupou from their practice squad.
Hill, 25, is a former second-round pick of the Bengals back in 2014. He’s currently in the final year of his four-year, $3,753,602 contract and stands to make a base salary of $881,855 for the 2017 season.
Hill will be an unrestricted free agent next year.
In 2017, Hill appeared in seven games for the Bengals and rushed for 116 yards on 37 carries (3.1 YPC) to go along with four receptions for 16 yards receiving and no touchdowns.
Koehn, 25, wound up signing on with the Dolphins as an undrafted free agent out of Iowa back in 2016. He was waived coming out of the preseason and unfortunately sat out the entire 2016 season.
The Vikings signed him to a future/reserve contract this past January but he was once again cut loose at the start of the regular season.
Koehn signed on with the Bengals last week while K Randy Bullock was dealing with an injury.
In 2017, Koehn appeared in one game for the Bengals and converted one extra point attempt.