Don't Expect a Major Announcement
It is unlikely that Treyarch or Activision will give users a big warning about a December Call of Duty: Black Ops 3 patch. The most you can hope for is a message from David Vonderhaar, Treyarch Studio Design Director, on Twitter a few minutes before the update arrives.
Vonderhaar shares information on the hotfixes that roll out, including the latest small fix that simply turns off Double Weapons XP in Call of Duty: Black Ops 3.
After the December Black Ops 3 patch is live, we may see an update to the support documents that tell us everything that is new.