The M4A4 is a rifle featured in Counter-Strike: Global Offensive.

The M4A4 is a rifle featured in Counter-Strike: Global Offensive. It is intended to replace Maverick M4A1 Carbine from previous Counter-Strike games. The M4A4 does not have an attachable silencer or any alternate fire unlike the M4A1 from the previous games.

Before an update was implemented, the M4A4 HUD kill icon still featured the old M4A1 HUD icon from the older versions of Counter-Strike.
Furthermore, as seen in the old Counter-Strike: Global Offensive trailer, the player model of the M4A1 was used for the M4A4.
The M4A4 is the only somewhat fictional weapon in Counter-Strike: Global Offensive by name (M4A4 Sherman is a tank designed and made during World War II). The naming scheme "A4" most likely comes from the misnomer of the M16A4.
The M4A4 is based on the Mark 18 Mod 0, which is a modified M4A1 equipped with the Close Quarters Battle Receiver, or Bushmaster M4 Type Carbine, which is a reproduction of the Colt M4 Carbine for civilian and law enforcement markets.
The M4A4 originally had a different firing sound, but during the developement of the game, it was changed to sound much more like the original M4A1.
The M4A4 shares its reload animation with the SCAR-20. Due to this, these weapons are the only assault rifles to share the same animations.