On X, L0vertodream also posted on X a Mac mini teardown. L0vetodream states that “it is indeed a 1-slot dual-slot with a maximum particle size of 1TB. It uses a BGA315 hard disk and the maximum upgrade capacity can be up to 2T” [translated].

Apple isn't soldering the SSD to the logic board in the M4 Mac mini, but given the company's history with Apple Silicon, don't expect upgrades.

The M4 Mac mini is a huge upgrade from its predecessors in a lot of obvious ways, with a faster processor, a tiny form factor and 16GB RAM as standard. Now some teardowns are showing that it’s also improved on the inside.