Five days after Early Access opened, Bulkhead put the next number on the Steam news hub:
2 million copies sold. The post is shorter than the first one and drops the apology —
Thank you all. Beyond humbled. We made a game we wanted to play with friends. Watching you play
it with yours has been the best.
— with a sales snapshot attached as an image rather than typed
into the post itself.
The number this site has not read first-hand
Games-press coverage on 17 September, syndicated from what reads as a studio press release, cited a new concurrent-player peak of 428,666, up from the 340,171 this site logged on 11 September. No outlet gave an exact timestamp — the figure is reported as landing "a few days" before the 17 September pieces went up, which points at 13 September without confirming it.
That number is not on the Steam news hub, and it is higher than anything this site's own read of Valve's API has recorded. It is carried here as Reported, not Confirmed, for that reason. The live tracker takes its own reading from Steam on every load and keeps the highest figure it has actually seen; if 428,666 is real, the tracker will catch it the next time the count gets there.
Against the first 1.25 million
The first-day post covered 1.25 million copies and a queue that was still being worked through as it went up. Five days on, the queue problems from launch night are not part of this post at all — the only operational item in the same window was Patch 0.11, a server-browser rework rather than an availability fix. Read together, the two posts track a launch that solved its access problems fast and kept selling after it did.