Watch the August showcase and the answer takes care of itself: characters push through doors into convenience stores, apartments and staff-only rooms without the screen fading, and walk back out the same way.
What the footage actually shows
Several categories of interior appear:
- Convenience stores and small shops with stocked shelves and staff behind the counter
- Residential interiors, including rooms that are clearly not safehouses
- Back rooms and stockrooms reached through service doors
- Bars and diners with people inside using them
Crucially, other characters use these spaces too. People walk in and out of doorways the player has not touched, which is a different design goal from GTA V, where an enterable building was usually a mission set piece or a shop menu.
Every building?
Almost certainly not, and Rockstar has not claimed otherwise. No open world of this scale models every interior, and the number of doors that open is exactly the kind of detail studios avoid quantifying before launch. What has changed is the ratio: enough interiors are live that walking into a building stops being a special event.
Why the loading screens disappeared
Both launch consoles use fast internal storage, which is what makes streaming an interior in while you are still walking through the door practical. GTA V had to fade to black on the Xbox 360 because a hard drive could not feed the geometry in fast enough. That constraint is gone - see our hardware notes for what the consoles are working with.
What is still unknown
Whether interiors persist - a shop you robbed staying wrecked, an apartment keeping the mess you left - has not been discussed. Neither has how many are randomly generated versus hand-built. Those answers usually arrive with reviews.
More on the world itself is on the map page, and the full showcase is linked from trailers.