After some confusion as to whether the storied «A-Life» simulation system was still present in Stalker 2: Heart of Chornobyl, GSC Game World has confirmed that it is—and also that, yes, it's got some issues, and also yes, they're working on it.
For those new to the world of Stalker, A-Life is essentially the underlying system of simulations that governs the behaviors and interactions of NPCs and monsters in the game. «The gist of the A-Life is that the characters in the game live their own lives and exist all the time, not only when they are in the player’s field of view,» OG Stalker programmer Dmitriy Iassenev said in a 2008 interview about the original Stalker with AIGameDev (via the Wayback Machine).
A-Life is ambitious, powerful, and—surprise!—janky as hell. It's also central to the Stalker experience: For as weird and glitchy as they get, the Stalker game worlds feel alive to me in a way that no other game has matched.
When something funky happens that obviously wasn't supposed to happen, it's often equally clear that it could have happened in the messy stew of the Exclusion Zone, and the fact that it did happen kind of makes sense—and as often as not those unexpected outcomes brought me an odd sort of joy.
There was, and persists, some confusion over whether A-Life had returned in Stalker: Heart of Chornobyl, expressed across numerous posts about it on the Stalker 2 subreddit.