Mosley has started every game he has played for the Ravens since being taken in the first round of the 2014 NFL draft. The Alabama product has earned four Pro Bowl selections in five seasons, leading the team with 105 tackles in 2018.
He has topped 100 tackles four times in his career and was named second-team All-Pro by the Associated Press in each of those four seasons.
The two sides still have a chance to negotiate a new deal, but Mosley will also get a chance to speak to all 31 other teams.
With the franchise tag, his rights would have remained with Baltimore through at least 2019. However, he would have received $15.443 million for 2019 without a new contract, according to Josh Alper of Pro Football Talk.
The 26-year-old made $8.71 million in 2018 in the final year of his rookie deal after making $8.78 million in his first four years combined, per Spotrac.
While letting him go could be a risky move for the Ravens, the team has remained confident on its ability to re-sign its star defender.
"There are limitations with the money, but C.J. wants to be back and we want him back," head coach John Harbaugh said in January, per Jamison Hensley of ESPN.com.
"I certainly hope that C.J. is back," new general manager Eric DeCosta said in February, per Hensley. "I believe in my heart that he will be."
Jamison Hensley @jamisonhensley
Ravens decline to use franchise tag on C.J. Mosley, per @AdamSchefter. History says Baltimore will still find a way to keep him. In their 24-year history, Ravens have never let a first-round pick who reached multiple Pro Bowls go elsewhere after his rookie deal expired.
More competition for Mosley's services could make re-signing him more challenging, however.