The chat app, founded in 2016, attempts to encourage engagement by automatically clearing out old content. It emphasizes polls, announcements and events in a way that makes its users more likely to respond, according to Sphere.
"Our work has always been guided by the belief that creating an online space where meaningful conversations can flourish is one of the most worthwhile challenges of our time," the company wrote in a blog post on Wednesday. "That's what brought us to Twitter. There are only a few companies today who believe in this vision and are in a position to make meaningful progress towards it."
Sphere will wind down its own independent app and 20 of its employees will join Twitter on its Communities, Direct Messages and Creators teams.
Nick Caldwell, the vice president of engineering at Twitter, also announced the acquisition on his Twitter feed.
"The Sphere team's expertise and leadership's passion for finding ways to help people connect will help accelerate our Communities, DM, and Creators roadmaps," he tweeted.
Neither Twitter nor Sphere announced the terms of the deal. Twitter didn't immediately respond to a request for additional comment.