Twitter began ranking tweets algorithmically in users’ home timelines in 2016.
Before the change, Twitter’s main timeline was commonly understood as a reverse-chronological stream. In February 2016, the company introduced an optional “show me the best tweets first” setting that placed selected posts near the top based on relevance and engagement signals.
Twitter later made algorithmic ordering more prominent and continued to offer users different timeline controls. The change was intended to help people catch important posts they might miss when following many accounts or returning after a period away.
This date is sometimes confused with later interface changes that altered how the default timeline behaved. The key 2016 development was the introduction of ranked “best tweets” above the ordinary chronological stream, not the invention of every ranking system used by Twitter.