Steam is good at many things but it appears that keeping information secret is not one of them as the date and duration of Lunar New Year sale of 2021 has been leaked.
Lunar New Year sale on Steam will start on February 11 and will last until February 15, 2021. The information comes from SteamDB but apparently originates from an internal email at Valve.
On top of that, the Lunar New Year will be on February 12, 2021, so there is little to no reason to doubt the legitimacy of the leak at this time. Still, it has not been officially confirmed so there is a small chance the sale might happen on a different day.
Some gamers may not be entirely sure that the information is legitimate and SteamDB's tweet announcing the sale does bear Year of the Rat promo image while it's going to be Year of the Ox this time around. The reason for this is that the start date info is a leak, not an official announcement, and as such, there is currently no promo art to be found for the event.
While this is the next big sale on Steam, it will be preceded by another one at the start of February. Game Festival: February 2021 is supposed to start on the third day of the month so prepare your wallets for ruination when the sales start kicking in.