According to Japanese Outlet Gamer, Final Fantasy XVI has sold around three million copies within the first week of its launch.
Interestingly, Final Fantasy XV sold an estimated 2.65 million first week at retail, but that figure includes multiple different platforms since Final Fantasy XV launched on Xbox, PlayStation, and PC. If we include digital numbers, the sales likely eclipse that of Final Fantasy 16, but it's still amazing that a console-exclusive Final Fantasy title would sell that well.
Final Fantasy 16 launched last Thursday, June 22, to critical acclaim. It was reviewed extremely well and is still dominating the conversation online. From people thirsting after Cid to people discussing the story of the game, you can't really move online without discussion of the game. As a timed console exclusive, it'll be extremely interesting to watch the sales and see how they tick before the game is inevitably ported to other platforms like with Final Fantasy VII Remake, which eventually came to PC along with being ported to PlayStation 5.