Stud career
Curlin covered 131 mares in the 2009 breeding season. The first foal he sired, a filly out of Zophie (Hawkster), was born on January 12, 2010, and was euthanized on January 29 after a paddock accident. Among other mares, Curlin was bred to the 2009 American Horse of the Year, Rachel Alexandra. During the broadcast of the 2011 Kentucky Derby, it was announced that Rachel Alexandra was expecting a foal, due around February 2012. A bay colt later named Jess's Dream was born on January 22, 2012, and won his first race on August 24, 2015.
Curlin was the leading third crop sire in North America in 2014. On September 2, 2015, Stonestreet Farm announced that he would stand the 2016 breeding season at Hill 'n' Dale Farm. Though his offspring tend to be somewhat slow to mature, Curlin is now regarded as a source of classic stamina.
In 2016, Curlin finished second on the North American general sire list. His stud fee for 2017 was increased to $150,000.
In 2022 Curlin's fee at Hill 'n' Dale Farm was $175,000. He was the leading sire at the 2022 Breeders' Cup with three winners on the Saturday card: Malathaat in the Distaff, Cody's Wish in the Dirt Mile, and Elite Power in the Sprint. At the end of that year, Malathaat won the champion older dirt female Eclipse award for her 2022 campaign, Elite Power won champion sprinter for winning 5 out of 6, and multiple grade 1 winner Nest, who also finished second in the Belmont Stakes, won the Champion 3-year-old-filly Eclipse award. Curlin is the first sire in the 52 years of the Eclipse awards to be represented by three different champions. His 2023 stud fee increased to $225,000 after the Breeder's Cup and Eclipse award success. After the 2023 Breeder's Cup results where Idiomatic, Cody's Wish, and Elite Power won their respective races, his 2024 stud fee jumped to $250,000.
His biggest stamp as a sire of runners came at the end of the racing season in 2023, when three of his offspring won individual Eclipse Awards, making him the first sire to achieve that feat as well. His 2025 stud fee was announced at $225,000 for the 20-year-old stallion, and it remained at that level for 2026.
At the 2026 Kentucky Derby, Curlin was the sire of first-place Golden Tempo, the damsire (through his daughter Spice is Nice) of second-place Renegade, and the grandsire (through his son Connect) of third-place Ocelli. Golden Tempo and Renegade were also first and third at the 2026 Belmont Stakes.
In 2026, Curlin was relieved of stud duty due to declining fertility. His stud fee was marked private by Hill 'n' Dale Farm for 2027.
He has 20 sons standing at stud, with Good Magic having the best success so far with two 3-year-old G1 "Classic" winners in Mage (Kentucky Derby) and Dornoch (Belmont), who are full brothers. He also has G1 winners Mixto, Muth, and Blazing Sevens. His son Keen Ice sired the winner of the 2022 Kentucky Derby, Rich Strike.