Yeah. Even for small structures like a garden shed, or a slab for a barbeque, it's always 4" min, and for an actual home, it's 6" min.

There are foundations that don't need a thick pour, like a raft foundation, where the actual footings can be 10" thick, but then the rest of the area is covered in just one or two inches, basically just to keep the dust and dirt down, but those types of foundations wouldn't be used for a basement that's meant to be occupied. At most, it would just be a crawlspace.