The Last Autumn is a prequel scenario centered at "Site 113" somewhere across the North Sea, where the British Empire has begun work on the first generator in preparation for the global winter. The DLC includes a new variant for Endless Mode, new technology trees and resources, new buildings (including a telegraph station, labour unions, and docks), new Books of Law to determine societal changes moving forward, and new threats to the settlement, including toxic gas leaks and worker strikes. It was released on January 21, 2020.
Source: Wikipedia, "Frostpunk", available under the CC-BY-SA License.