TL;DR: After August 31, 2018, CircleCI 1.0 will no longer be available for Linux and macOS users. You can find guides for transitioning from 1.0 to 2.0 and a full timeline on planned changes here.
We launched CircleCI 2.0 for general availability in July 2017, providing users with increased flexibility, power, and control. Since then, build times on both our Linux and macOS fleets have been dramatically reduced. We’ve been able to handle increasing numbers of users and jobs, while simultaneously decreasing average job time across every language we serve. The addition of Workflows in 2.0 has also made it possible to match your pipeline to your team’s needs.