There's no listed expiry date on the free Aliens vs Predator Classic 2000 offer, but the "limited availability" suggests to me that availability is limited, so grab it while you can.

Predator: Hunting Grounds is launching a free trial for players this weekend. You'll be able to jump into the asymmetrical shooter starting today until Sunday, March 27-29, ending at 11:59 PM.

The franchise, which has spanned several movies and comics, became a critically acclaimed first-person PC game in 1999 that allowed players to play as either a Predator, Alien or human soldier.