"The first matchmaking update for Reach will occur in early October and consist primarily of fixes for bugs and balance issues," said the firm.
"We're not done testing them all yet, but when they're ready we'll fill you in on all of the little details. We'll also be adding some game types and Forge maps. Co-op campaign will be going live in October as well."
Matchmaking wasn't available in Halo: Reach from the start because Bungie was worried about it spoiling the single-player mode, as players could potentially jump right in at the end of the game.
You can check out the full Bungie update.