Expect multiplayer to arrive in a the next few months.
Sniper Ghost Warrior 3 is out today but the multiplayer portion of the game has been put on hold.
A statement from CI Games explains that the team is aiming to "provide the best possible single player experience in our most ambitious game [in the series] to date."
Post launch content is another priority, with regular updates to follow after release.
"Therefore, we have chosen to release the multiplayer update (that will be free for our players) after launch (the third quarter of 2017) for precisely the above reasons, that is not to dilute any potential from the single player experience."
So not to worry, the multiplayer is still happening. You'll just have to wait a while.