The software behind planet.archlinux.org was implemented in Python 2 and is no longer maintained upstream. This functionality has now been implemented in archlinux.org's archweb backend which is actively maintained but offers a slightly different experience.
The most notable changes are the offered feeds and the feed location. Archweb only offers an Atom feed which is located at [here](https://archlinux.org/feeds/planet).
URL: https://www.archlinux.org/news/planet-arch-linux-migration/
arch-announce@lists.archlinux.org