A single developer who can complete projects in the same amount of time as 10 or 100 or 1000 regular developers to at least the same quality standard (but usually to a higher quality standard because code quality is key to getting that productivity gain in the first place and code quality usually translates to project quality).

That said there are projects for which a developer could be infinity-x compared to other regular developers. For example, a highly complex project which regular developers do not have the capacity/talent to complete, ever... Just imagine some very complex project programming a quantum computer or certain kinds of blockchain or distributed systems projects; some developers will never be capable of delivering such projects. It's beyond their innate ability and capacity for learning.

Project complexity maximizes the utility value of highly productive developers. It would be difficult to identify a 100x developer on a simple project (they might only appear as 2x) but they would stand out as a definite 100x on a complex project.