The codename of Ubuntu 21.04 has been revealed and it is Hirsute Hippo. Along with the codename development of Ubuntu 21.04 is now officially started.
Ubuntu developer Matthias Klose posted a message over Ubuntu developer mailing list regarding the announcement:
Hirsute Hippo is now open for development, with the uploads collected in the queue now approved, and syncs from unstable enabled. The development version starts with one change: - Python 3.9 is now added as a supported Python3 version, with the goal to ship Python 3.9 as the only Python3 version in hirsute. Please check your uploads in a hirsute chroot, don't just test in a focal or groovy environment. See [1] or [2] how to setup such a development chroot. Some major changes planned for this cycle are mentioned in the Hirsute release schedule [3].