Here you will find the release notes for all Zircon releases.
A new Zircon version is released: 2021.1.0-RELEASE
A new Zircon version is released: 2020.2.0-RELEASE
A new Zircon version is released: 2020.1.0-RELEASE
A new Zircon version is released: 2018.12.25-XMAS.
A new Zircon version is released: 2018.5.0-RELEASE.