Uncharted 4 has gotten a new major update on the PS4 which brings the new Survival mode. Survival is a co-op mode where up to 4 players work together to beat waves of enemies.
Survival features up to 50 waves of enemies, with boss battles in between, and more. The mode even features a singleplayer mode, where you can take on the waves alone.
In addition to Survival, the new update adds two new maps: Train Wreck (from Uncharted 2), and Prison. Some new weapons are added as well, including the classic M4 assault rifle, PAK-80 Light Machine Gun, and the Desert 5 pistol (Desert Eagle).