https://blog.ethereum.org/2021/11/10/arrow-glacier-announcement/
Arrow Glacier Upgrade Announcement
Posted by Tim Beiko on November 10, 2021
"The Ethereum network will be undergoing a scheduled upgrade at block number 13,773,000, which is predicted to occur on Wednesday, December 8, 2021. The exact date is subject to change due to variable block times and timezones. Please upgrade your node before Wednesday, December 5, 2021 to account for the variable block times."