Endnight Games' Sons of the Forest was only in Early Access for a full day and managed to sell 2 million copies. The developer announced the milestone on Twitter, saying it was "very excited for what we have in store for players in the coming weeks." 

Sons of the Forest is the sequel to 2018's survival horror game The Forest. The original game came to Early Access in 2014, and sold 5 million copies by the end of 2018 across releases on PC and eventually PlayStation 4. 

When Sons of the Forest had its early release on February 23, it opened to 250,000 concurrent players on Steam. According to SteamDB, the title currently has over 234,000 concurrent players (at time of writing), and has previously had a 24-hour peak of over 365,000 players.

Endnight has previously said it wants Sons' Early Access period to last around 6-8 months before a full release. Whether or not those plans stick, the amount of sales for Sons of the Forest so far indicate good things for its eventual full release, and Endnight's future as a horror game developer.