Long, long ago, in a galaxy far, far away, Twitter provided a firehose of data to a few of partners and the world was happy. These startups were awash in real-time data and they got spoiled, some might say, by the embarrassment of riches that came through the real-time feed. Over time, numerous factors caused Twitter to cease offering the firehose. There was much wailing and gnashing of teeth on that day, I can tell you!
At roughly the same time, Twitter bought real-time search company Summize and began offering to everyone access to what is now known as the Search API. Unlike Twitter’s existing REST API, which was based around usernames, the Search API enabled companies to query for recent data about a specific keyword. Because of the nature of polling, companies had to contend with latency (the time between when someone performs an action and when an API consumer learns about it) and Twitter had to deal with a constantly-growing number of developers connected to an inherently inefficient interface.