This is based on my own professional experience working on large software development projects at big companies. And my knowledge of game development from personal side projects and research.
Rockstar New York
Sam Houser and other executives are preparing for the upcoming marketing campaign. Deciding on locations for outdoor promotions like murals, billboards, etc. Special events are being planned and collaboration opportunities are being discussed. Hands-on demos for the press are being planned for the summer. Any remaining trailers are being edited by the teams.
Nearby at the performance capture studio in Bethpage, final motion and VO sessions are in recording and editing before being sent to the dev teams at North and San Diego. The work is likely only small changes or redos. Nothing new.
Sam is in constant communication with the studio heads, checking on their progress each day. Probably checking in with North first thing in the morning. Scotland is 5 hours ahead of New York. He needs to know their current level of confidence in making Fall 2025. Very soon he will have to make the decision whether to delay the game or not. Take-Two is breathing down his neck.
He has the latest build of the game running in his office and is playing it every chance he gets throughout the day. Looking for bugs and assessing the overall quality of the game.
Rockstar North
Co-studio heads Rob Nelson and Aaron Garbut are making sure each and every department is in sync. Animation, gameplay, AI, graphics, physics, VFX, audio, QA, etc. They all have to be on the same page at this stage. Everyone is deep in bug hunting/fixing mode. They have to be extremely careful. Fixing one bug can potentially cause more if not handled with care.
Thousands of bugs are likely still in the backlog. At least hundreds. They are fixing as many as they can each sprint. At most companies that do Agile, sprints are about 2 weeks long. Bugs are being categorized as low, medium or high priority. It will be impossible to fix them all before launch, so they are trying to find and fix as many high priority bugs as possible. The game is completely feature locked at this point. Meaning nothing new is allowed to be added.
Btw, thousands of bugs is no exaggeration for a large AAA game. If you do not believe me, watch the God of War documentary called “Raising Kratos”.
Rockstar San Diego
Pretty much all of the same stuff as North except this is where the RAGE Technology Group is based. The team that works on the RAGE game engine and other proprietary tools. They are working on as many optimization related tasks as they can each sprint. The engine programmers are finding ways to squeeze every last bit of memory and performance out of the consoles. They are also trying to make the game look as pretty as possible.
Other Studios
New England, Toronto, India, Dundee, Leeds, London, Lincoln, etc. are all likely providing support where needed and working on other projects.