From a blog post by Twitter search infrastructure engineer Yi Zhuang:

Since that first simple Tweet over eight years ago, hundreds of billions of Tweets have captured everyday human experiences and major historical events. Our search engine excelled at surfacing breaking news and events in real time, and our search index infrastructure reflected this strong emphasis on recency. But our long-standing goal has been to let people search through every Tweet ever published.

Twitter search has long been incomplete because the company’s engineers focused on the real-time feed, about a week’s worth of public content on the service. Zhuang’s blog post goes into great detail about “how we built a search service that efficiently indexes roughly half a trillion documents and serves queries with an average latency of under 100ms.”

Twitter says the change will be rolling out on desktop and mobile app versions of Twitter in the next few days.