First-person engineering sandbox Satisfactory launched in early access on Epic in March of 2019. A month ago it became available on Steam as well. In the interests of transparency, Jace Varlet, community manager at Coffee Stain Studios (who are also responsible, lest we forget, for first-person tower defense series Sanctum, and Goat Simulator, as well as publisher of Deep Rock Galactic and Huntdown) has shared the numbers.
I recommend watching the entire video to see Jace humbly thank players for their support, it's very wholesome and nice. But if you just want the data, here you go: 1,326,518 copies sold total, with 958,917 on the Epic Games Store and 367,601 on Steam. As Jace explains, "Epic sold in about three months or something 500,000. The total number sold on Steam in a month or whatever is 360,000 so it's slated to probably overtake what Epic did at that time."
Jace notes there are a lot more people using Steam than Epic, which is the obvious explanation for why Satisfactory's already good sale numbers are probably about to be bettered, but there's more to it than that. "Another thing to consider is that there has been the Summer Sale, and we have been on the top sellers. We were at first or top three for a very long time and we're still in the top 10." That exposure is always good for sales, resulting in the cycle where Steam's best-selling games continue being put in front of customers and selling more copies and staying high in the list. "Another thing to consider is Satisfactory is a better game now," Jace says. "There's more features, it has had one more year of exposure."
It's a nuanced explanation of what it's like to have a game on both storefronts, data that will now be picked up and used as a blunt instrument by people with grudges against shops because this is the internet after all.
The final thing to note is that Satisfactory really has sold extremely well, no matter which storefront you're looking at, even by the standards of the people who made Goat Simulator. Over a million copies for a game that doesn't have the backing of a major publisher—a game that is about constructing assembly lines and then constructing more efficient assembly lines—is worth congratulating.
If you'd like to know more about what it's actually like to play, here's Wes on the joy of making alien factories more efficient.