Technically four if you want to include the new Nazi Zombie map, which takes place in a secret facility. It's a patch so things like "various crashes" get fragged; always a good thing.
"Great news - Patch 1.6 (w/ Map Pack 3) is finished & now in test over at Activision!" posted Treyarch's community man 'JD'.
"Additionally, we do expect a concurrent release of the Mod Tools 1.4 package, Linux dedicated 1.6 bins, and the Steam 1.6 day-of-date with this patch. More details on those will be made available once they get cleared through testing."
See below for a full list of changes coming with patch 1.6 this week.
• 3 new Multiplayer maps: Battery (mp_drum), Breach (mp_bgate), Revolution (mp_vodka)! • New Nazi Zombie map: Der Riese (nazi_zombie_factory), an all-new Zombie map set in a secret Nazi research facility featuring the Pack A Punch Machine, Teleporters, and many more undead hordes! • Exploits pertaining to Demo playback. • Favorites list now ignores filter settings. • Fixed S&D round counting error when roundlimit is reached. • New feature: in-game Add to Favorites. • Friends list: green online indicator. • Starting the game in Safe Mode will no longer toggle the “Soften Smoke Edges” graphic option. • Fixed various crashes. • Mods: Client will no longer join a modded Co-op server via Game Invite unless they have that mod loaded. • Mods: Client running a mod will be asked to unload the mod if they attempt to join an unmodded server. • Mods: All singleplayer levels can now be run with a mod loaded.
Source: Eurogamer