X4 Foundations is the base game. There are four expansions you can add:

• Cradle of Humanity: adds the Sol sectors and the Terran faction
• Split Vendetta: adds the Split faction and sectors
• Tides of Avarice: adds the Windfall and Avarice sectors, and the Vigor Syndicate and Rakers factions
• Kingdom End: adds the Boron faction and sectors

DLC’s add more content, but they don’t change the game (with a few small exceptions). They are “more of the same” for people who like the game. They expand the universe with more factions to interact with and more sectors to explore.

You can add the DLC into the base game at any time, including installing them and continuing an existing save. You do not need to start a new game.

What do the DLC give me?

The DLC provide more sectors, more optional-but-interesting plot lines you can pursue, more “races” with their own ship types.

They don’t change game play mechanics (how the game works, what player can do, etc).

Some do add some small additional mechanics, but they are additions, not changes. The existing content and game mechanics still works exactly as before, alongside the new addition. Example: the Kingdom End expansion adds some Boron weapons that have a new effect, slowing ships when hit. The new boron weapons do this, but existing weapons don’t gain this attribute.