DICE was nice enough to unlock the 64-player Caspian Border map for PC beta testers today.
According to ArsTechnica, players were given a bit to play on the map before the server went down.
A password to enter the server running the map was handed out by a DICE community manager on the official form, and the password was changed at 18:00 CET.
Ars expects the next password to appears either again on the forum or through Twitter, but with only two servers running the map only 128 people can play the map at one given time.
In other words, keep your eyes peeled for your chance.
Operation Metro is the official map available in the Battlefield 3 beta.