Not only the annual sales campaigns, but also the premature leakage of the appointments for these are already a long-standing tradition at Steam. The generally well-informed Steam Database gives the alleged data for the Halloween Sale, as well as the autumn and winter action.
Thus, the next discount battle for games with the Halloween Sale starts already in a week on 28 October and ends on 1 November. From November 26 to December 3, the Atumn Sale will take place, which is usually called Herbstaktion in this country. The annual Winter Sale aka Christmas promotion is scheduled to begin on December 19 and end on January 2, 2020.
Leaked upcoming @steam_games 2019 sale dates:
? Halloween Sale: October 28 – November 1
? Autumn Sale: November 26 – December 3
? Winter Sale: December 19 – January 2
Valve asked otherwise. But you know how that goes.
– Steam Database (@SteamDB) October 19, 2019
As so often the dates should come from circles of game developers, who are informed in advance by Valve about upcoming Steam Sales, but should actually keep the information to themselves.
At the competitor Epic Games Store the Halloween Sale has already started and runs until the 1st of November. Also in GOG.com and Humble Bundle is expected in the coming days with appropriate discounts.