Twitter does one very specific thing, and it doesn't look like it has changed its goal much over the past 10 years, so what is it they're trying to develop so rapidly they need hundreds (thousands?) of developers.
> One occasionally reads newspaper accounts of how two programmers in a remodeled garage have built an important program that surpasses the best efforts of large teams. And every programmer is prepared to believe such tales, for he knows that he could build any program much faster than the 1000 statements/year reported for industrial teams. Why then have not all industrial programming teams been replaced by dedicated garage duos? One must look at what is being produced. In the [attached figure] is a program. It is complete in itself, ready to be run by the author on the system on which it was developed. That is the thing commonly produced in garages…
He then goes on to describe how you can take a program and make it a programming product (by generalizing it, adding testing, documentation, maintenence) and a programming system (requiring interfaces and integration with the rest of the system)
Though I think the number of developers are still too high.