GO onto Steam, unlisted on the store page, which you can download and play now via direct connecting to servers.
Valve has given Counter-Strike Global Offensive its own page separate from CS2, but you can't search the Steam store for the classic FPS.
CS:GO was subsumed into Counter-Strike 2 a few years ago, but now it has its own Steam page again.
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You can play CS:GO on Steam again, here’s how

When Valve dropped Counter-Strike 2, there was one major disappointment: not being able to go back to Global Offensive. Now, there’s a change! “CS:GO is back on Steam! This is real, I did not make ...
Valve has officially brought Counter-Strike: Global Offensive (CS:GO) back on Steam. The game’s Steam store page was replaced by Counter-Strike 2 when the latter sequel (or reboot, depending on who ...