No choke from the factory, 12-gauge, cylinder bore is 0.730 inches
The Saiga 12 was designed for screw-on chokes.
Carolina Shooters Supply sells them individually or in a set of three.
https://www.carolinashooterssupply.com/SGM-SAIGA-12-Full-Mod-X-Full-CHOKE-SET-VEPR-12-p/sgm-s12-3pc-choke.htm
CSS also sells a Saiga flash hider that is designed to take certain Winchester win-Chokes.
https://www.carolinashooterssupply.com/CHOKE-ADAPTER-10-SLOT-SAIGA-FLASH-HIDER-VEPR-p/cncw-choke.htm