Yup, Gears of War 3 is the game Cliff Bleszinski premiered for the Late Night With Jimmy Fallon audience. And depending on what coast you're on, you may have already seen it.
But why turn on your TV? The Late Night with Jimmy Fallon blog has posted the trailer (called "Ashes to Ashes") online, and you can go watch it right now. (It's about two minutes in.)
The trailer shows off an ashen world where the battle continues to rage on between the Locust Horde and Marcus Fenix along with his crew of merry men. And yes, there appears to be some sort of enemy with tentacles... no mech suits, though.
Sun Kil Moon's "Heron Blue" serves as the soundtrack to the trailer, evocative of the original Gears of War "Mad World" spot.