Cloud Imperium Games will be splitting apart Star Citizen and its single-player experience Squadron 42 this month. It was announced back in December that, while both occupy the same universe, it was better if they stood by themselves.
This means that anyone who has pledged up until the day of the split will get both Star Citizen and Squadron 42, but after you'll need to purchase Squadron 42 as an optional add-on. Star Citizen is the persistent universe or MMO-style multiplayer version where players can mingle with others, whereas Squadron 42 is more akin to the story-focused Wing Commander.
"At the December livestream, we announced that Squadron 42 and Star Citizen will be split into two separate packages in the near future. To update on this: the split will occur on February 14th. Squadron 42 will be available as either a stand alone game or an optional addon for Star Citizen rather than be included by default. If you want to lock in both games for the lowest possible price, consider pledging before this deadline."
Squadron 42 has grown in size since the initial Kickstarter campaign with tens of millions of dollars resulting in a much larger and grander scaled story campaign with a rich cast of talent filling major roles such as Gary Oldman, Mark Hamil and Gillian Anderson.