Are Oracle and Carnac closed?

Yes, to new registrations. The post on Knight Online's official X account (21:58 UTC) thanked players for the rush and said the two servers were shut to sign-ups to keep the servers balanced. Existing registrations aren't mentioned.

Official announcement image: pre-registration for Oracle and Carnac is temporarily closed
Image: NTTGame
Source / rights
Image / usage information: © NTTGame / Mgame. Official Knight Online announcement images, used for game reporting. · Image source ↗
Short answer

NTTGame temporarily closed pre-registration for Oracle and Carnac on November 6 because of heavy demand. New players can now only register on Atlas and Luna; no reopening date was given.

Which servers can you still register on?

Only Atlas and Luna. Sixteen minutes later NTTGame posted that pre-registration for those two is going full speed, through the new server registration page.

Source · www.nttgame.comKnight Online new server pre-registration

New server registration status (November 8)
ServerPre-registration
Oracle Temporarily closed
Carnac Temporarily closed
Atlas Open
Luna Open
Official announcement image: pre-registration for Atlas and Luna continues
Image: NTTGame
Source / rights
Image / usage information: © NTTGame / Mgame. Official Knight Online announcement images, used for game reporting. · Image source ↗

Why did Oracle and Carnac fill up?

The community list of streamer and clan picks explains it: 34% of streamers picked Carnac and 27% Oracle, and Oracle (141) and Carnac (113) also led in team count. Atlas had 84 teams and Luna 67.

I already registered on Oracle or Carnac. What now?

The notice only says pre-registration is closed; it mentions no change for people who already registered. If your registration is there, you don't need to do anything. You can check which server you're on from the registration page.

My team is on Oracle and I couldn't register. What do I do?

The closure is "temporary", but NTTGame gave no reopening date. Your options: wait for a reopening announcement on the official channels, or move to Atlas or Luna as a team. Each account can register on only one new server, so don't rush into the wrong one.

The servers open on November 12; times and character creation: new servers November 12 guide.

FAQ

Will Oracle and Carnac reopen?
The notice says "temporarily" but gives no date. A reopening would be announced on the official X, Instagram and nttgame.com; we'll update this page.
Will Luna and Atlas stay empty?
No. Atlas has 84 teams and Luna 67, and all new registrations now go to those two, so both are expected to fill up at launch.