Even IF Twitter could have been built with 30 developers (I have no opinion on whether this point is possible), I find it hard to believe that the system that

Even IF Twitter could have been built with 30 developers (I have no opinion on whether this point is possible), I find it hard to believe that the system that was built by several hundred people (several thousands?) can be maintained by 30 of them. This is not a commentary on the ability level of either groups. 20 developers are just about more than enough for one on-call rotation as well, so hard to believe how the numbers would work out. At Twitter scale and across all their systems, I do expect incident to happen daily.