Hacker News Reader

Im sure every company does it differently, but i heard that Valve has repository set up in a way that trunk is latest version of source engine and then they make new branch for each game.

There are various levels of that. You could have things damn near from scratch. You could reuse the same game engine (like Unreal). You could reuse more, where it’s mostly the same game code with new content. Civ 5 -> Alpha Centauri was like that. Then you can have expansions or DLCs that really are just additions.

I imagine (hope) this change is on the deeper side. GTA V is quite old.

Many studios maintain a game engine that is used across multiple titles. Often there is some shared code, especially for sequels, and especially when the sequels are frequently released.