Every entity represented in Twitter's API has an ID associated with it. As we allocate larger and larger numbers for these IDs, the space required to store them must grow in turn. For example, we migrated Tweet IDs from 32-bit to 64-bit integers back in 2009, then did the same for direct message IDs in 2011. We expect to start allocating user IDs in a 64-bit integer space sometime this year. This