In which class of airspace may a Part 107 remote pilot operate without any prior authorization?

Why →Class G airspace is uncontrolled airspace. Under Part 107, operations in Class G airspace do not require prior FAA authorization. All other classes (B, C, D, and E at the surface) require authorization via LAANC or a FAA DroneZone waiver.

The trap →Class E above 1,200 ft AGL is also uncontrolled in some respects, but surface-level Class E (common around smaller airports with instrument approaches) does require authorization.

Field note →Most rural areas, farmland, and open country are Class G from the surface. If you're far from airports and not under any depicted airspace, you're almost certainly in Class G.