CS2 vs CS:GO — what actually changed?

CS2 runs on Source 2 — the same engine that powers Dota 2 and Half-Life: Alyx. Source 1 was old enough to drive Valve's rendering, lighting and networking choices into a corner; Source 2 unlocks a lot of changes that weren't practical on the old base.

Smoke grenades in CS2 are real volumetric objects that react to bullets, HE grenades and the environment. Shoot through a smoke and you punch a brief hole in it; throw an HE into one and it temporarily dissipates. Old CS:GO smoke "one-ways" no longer work the same way.

CS:GO had 64-tick (and on third-party services 128-tick) servers, meaning the server processed the world 64 or 128 times per second. CS2 introduces "sub-tick" updates: the server timestamps your inputs to the moment they happened, regardless of tick rate. In theory, your shot lands when you pulled the trigger, not on the next tick boundary.

The competitive system was rebuilt. Old skill groups (Silver / Gold Nova / Global Elite) are gone. Premier mode uses a numeric CS Rating that goes up and down based on win/loss against your opponents' ratings, similar to chess ELO. Map picks and bans happen at the start of every Premier game.