In the end it comes down to your definition.
What is a AAA Studio?
Defined by employees and money spent per year?
Does that make a Studio like KING or Zyga AAA Studios?
or
Is a AAA Studio defined by making AAA games, which again are definied via Budget,Manhours & campaigning?
Let's have a look at a few companies.
-Is Firaxis AAA? With Civilization and XCom. With just about 200 employees they are actually relatively small. My guess their budget for games is rather high though.
-Is Amplitude AAA? It's actually extremely similar to Firaxis in terms of employees. My guess is that their budget mit be lower than from Firaxis, but thats just my guess.
-I think the majority will agree on Piranha Bytes Elex not being AAA. They just have 33 Employees. But they certainly have much more budget, using external companies for cutscenes and utilizing resources of their owner Embracer Group. Maybe even if the game would be called AAA, the tiny amount of just 33 employees would probably disqualify them as AAA company?
-Is CD Project Red AAA? I guess after Witcher 3 and Cyberpunk everyone would say so. Apparently Cyberpunk costed 263 Million USD and they have 1111 Employees.
So here we cot completely wild dimensions and magnitudes already. Firaxis and Aplitude are more than 5 times as big as Piranha bytes. And companies for "real" AAA titles are about more than 5 times more than that looking at CD Project Red, but also Productions like COD or Assassins Creed.
Larian's 400 employes (stated by Sven in march 2022) working on BG3 already surpass Firaxis and Amplitude (or are on par, their numbers are more outdated). And of course surpass Piranha Bytes by a lot. And apparently their budget does as well.
Even the producer calls it AAA:
“I would call it a triple-A game. It has a triple-A budget, has a triple-A team by now, and I think that is our aspiration.”
Overall, I guess BG3 and Larian can rather be called AAA rather than not. While its still not quite at the level at CD Project Red or "the big ones", especially in terms of RPGs they are probably as AAA as it gets.