Obviously it is all unconfirmed by Steam, but there is good reason to give the info credibility.
The word on the street, and by street I very much mean Reddit, is that the 2016 edition of the Steam Summer Sale will begin on June 23 and run until July 4.
That word comes from an unknown developer who seems to have little interest in the finer points of confidentiality, who posted an image with the info. Oddly enough, the message is in english, but the dates themselves are in Russian, suggesting that the leak either originated there, or is fake.
Obviously this is all entirely unofficial and unverified, so take it for what it is worth, but also bear in mind that basically the same thing happened last year—the Steam Summer Sale dates were leaked onto Russian social network VK, by the same guy (Vyacheslav “MrFreemanBBQ” Konchits) who posted this years dates—and proved out to be accurate. I have reached out to Valve for confirmation of the dates, and I will let you know if I get anything back.
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