The servers will come down for an update on March 21, at 13:00 GMT/ 9:00 AM EDT/ 6:00 AM PDT. (check this link to see when this is in your timezone). The downtime is estimated to take 2 hours.
This thread was added on March 20, 2019, with posts from AndyB, Spynosaur_Nicole.
The servers are back up! Unconquered mode is now enabled. Patch notes and more details on this mode will be posted shortly.