Update: The deadline to migrate existing HTTP webhook URLs is being moved from Tuesday, December 4th 2018 to Tuesday, January 15th 2019.
In order to give teams some flexibility during the winter holiday season, the deadline to migrate existing HTTP webhook URLs is being moved from Tuesday, December 4th 2018 to Tuesday, January 15th 2019. All other details in the original changelog post remain unchanged.
Here is a link to the original changelog update; you can also join the conversation in the Developer Forums here.