MarsSeed [1] filed a deletion request for arduino-avr-core-rc [2]: Abandoned, but unneeded preview version package. Upstream hasn't published any non-stable release tags in 4 years. [a] Arch repo has a newer stable version. [b] [a]: https://github.com/arduino/ArduinoCore-avr/releases [b]: https://archlinux.org/packages/?q=arduino-avr-core [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/arduino-avr-core-rc/