There are multiple projects in this repo. Windows Terminal, which the other commenters focus on, is a relatively new standalone app and not (yet?) bundled with the OS. They opted to open source it from the start, more or less. The other part is conhost, which is the classical terminal that has existed in Windows for decades. Some of the layout and rendering logic was pulled out of conhost to be shared with Terminal, and the two projects are maintained by the same team, so they open-sourced both. As I understand it, they then ship conhost and its shared components in Windows releases.