In addition to the old Gun Master mode from Battlefield 3. The patch will add five new weapons, and while DICE didn't share their exact names and look, it gave us a general idea for what to expect:
New fan favorite Assault Rifle - Picked based on its unique burst gameplay and massive fan desirability (its the AN-94)
New Carbine - A unique bullpup carbine with built-in vertical grip
New PDW - A unique PDW with built-in silencer
New Sidearm - Unique long range “sniper” sidearm using magnum rounds
New LMG - Magazine fed LMG, which with the new weapons balance, plays in between a belt-fed LMG and an AR – your “run and gun” LMG
Gun Master, which gained its popularity in the Battlefield 3: Close Quarters DLC, is like Team Deathmatch, but you only get new weapons every time you get two consecutive kills, and the first player to get a kill with the final weapon wins.
The patch will also "significantly improve client stability on all platforms," fix a number of issues that cause crashes, and rebalance all weapons, which you can read about in greater detail here.
DICE said that it will release full patch notes once the update is released.
http://www.gamespot.com/articles/battlefield-4-patch-with-new-guns-and-mode-coming-/1100-6427556/