"I'm very appreciative for the 10 years of loyal service that Glenn Spencer gave to Oklahoma State," Gundy said.
Spencer has been with the program since 2008 but has served as the team's defensive coordinator since 2013.
The Cowboys finished the year 10-3 with a win in the Camping World Bowl, their third straight 10-win season and fourth in the last five years. The squad finished 14th in the final Associated Press poll.
However, the offense did most of the heavy lifting in the team's success. While the team ranked fourth in the country with 45.0 points per game, it ranked just 85th in FBS with 29.4 points allowed per game.
Oklahoma State ranked 19th in the country in scoring defense in Spencer's first year as defensive coordinator in 2013, but it hasn't finished in the top 50 since. While the team's pace and the Big 12 competition doesn't help, allowing more than 40 points in four games last year is reason enough to reevaluate the staff.
While Gundy has often found his coordinators internally, he has also shown he is not afraid to be creative in his pursuit of a new coach. Current offensive coordinator Mike Yurcich was found at Division II Shippensburg after the head coach conducted an internet search.
With the team also having to replace talented seniors Mason Rudolph, James Washington and others, there will be a lot of turnover in Stillwater heading into 2018.