Kubuntu 18.10 Cosmic Cuttlefish was released on October 18th 2018 with 9 months support. As of 18th July 2019, 18.10 reaches ‘end of life’. No more package updates will be accepted to 18.10, and it will be archived to old-releases.ubuntu.com in the coming weeks.
The official end of life announcement for Ubuntu as a whole can be found here .
Kubuntu 19.04 Disco Dingo continues to be supported, receiving security and high-impact bugfix updates until January 2020.
Users of 18.10 can follow the Kubuntu 18.10 to 19.04 Upgrade  instructions.
Should for some reason your upgrade be delayed, and you find that the 18.10 repositories have been archived to old-releases.ubuntu.com, instructions to perform a EOL Upgrade can be found on the Ubuntu wiki .
Thank you for using Kubuntu 18.10 Cosmic Cuttlefish.
The Kubuntu team.