It would appear many people wanted to brave the zone and tear their survival skills in Stalker 2 according to developer GSC Game World.
In a post sent out early this morning the developer proclaimed that their most recent release had sold a million copies since its release on Wednesday, 2 days ago. This is in addition to the many players enjoying it via Xbox Game Pass. The post reads:
"No wonder it feels a bit crowded in the Zone. A million copies were sold, and much more stalkers joined the artifact hunt with Game Pass.
This is just the start of our unforgettable adventure. The Heart of Chornobyl emanates stronger with each of us.
Thank You, stalkers!"

This is surely a huge milestone for the game as Stalker 2 has had quite the adventure to get to this point having been developed through the war in Ukraine. Considering the game is on Game Pass it's a great accomplishment. Over on Steam Stalker 2 has boasted a concurrent player count of over 117k making it one of the most played games on the platform.
Despite all of this the game has seen its issues with many reviewers saying it has many bugs. A lot of those bugs seemed to be addressed in a nearly 130gb patch but some issues still persist. In a message sent yesterday by GSC where they thanked fans for their support, they also said they will continue to support the game with free updates and fixes.
If you'd like to learn a bit more about the development of the game you can watch the previously released documentary on the game here.
With the start the game has had already, it's safe to say the Stalker 2 is already a hit.