Update: January 11, 2019
Now, Verizon rolling out December 2018 security patch for Galaxy S8 and S8+ as build number G950USQU5CRL2 and G955USQU5CRL2 respectively.
Original – January 3, 2019
First AT&T and now Sprint is also sending a new update for Galaxy S8 and S8 Plus, which only brings December 2018 security patch along with fixes to 40 Samsung Vulnerabilities and Exposures (SVE) items.
The Galaxy S8 and S8+ are receiving this update as build number G950USQU5CRL2, G955USQU5CRL2 respectively. If you want to check this update manually, head into Settings > System updates > Check for system updates or you can simply wait till the update automatically appears on your phone.