Although Valve hasn't made a big announcement regarding the start of the annual Steam Holiday/Winter sale, the company has confirmed the leaked dates through its Holiday Auction page.
"The Auction runs Dec 15 @ 10:45am to Dec 18 @ 1:00pm when the Holiday Sale begins," Valve says on the page of its unique Steam event.
While the company hasn't made a formal announcement (they typically never do), an email from PayPal Japan revealed a start date of December 18th. A follow-up from Eurogamer added that the sale will run until Friday, January 2, 2015.
Valve doesn't usually announce its sales early, typically waiting for the day-of to just unleash the discounts. This typically causes the Steam Store to crash temporarily before finally stabilizing. So should tomorrow be the actual start date of the Holiday Sale, then expect an update around 1:00pm Eastern Time.
In preparation for the sale, Valve recently add their Holiday 2014 profile badge to the Steam market, indicating that this year's sale will continue the tradition of buying games, playing games, collecting cards, crafting badges (or selling cards), and so on. The page says the Holiday Sale 2014 trading card will be valid until January 2, offering further proof of the sale's end date.
In the meantime, Valve it's not too late to participate in the "Holiday Auction." This temporary event, which ends on December 18 at 1:00pm EST, involves users recycling Steam Community items like Trading Cards, backgrounds, and emoticons from their inventory into Gems and then using those gems to bid on games up for auction. Though there were some problems early on with players taking advantage of the system, it now appears to be working correctly.
As for the contents of the Steam Holiday Sale, we'll likely have to wait until tomorrow to find out the discounts, but expect the usual daily and flash deals. As always, we'll be sure to let you know when the sale goes live.