I received word from our friends at Tor Books that Greg Bear's second novel in his Forerunner Saga, Halo: Primordium, will be available in trade paperback on October 30th.
Here's the official word:
HALO: PRIMORDIUM is the second book in the New York Times bestselling Halo Forerunner Saga, written by legendary science fiction author Greg Bear. Halo: Primordium is also currently available in hardcover, e-book, and audiobook. The first book of the Forerunner Saga, Halo: Cryptum (Book 1) is currently available in trade paperback, e-book, and audiobook.
In Halo: Cryptum, Greg Bear began a three-book arc set in the era of the Forerunners, the ancient and enigmatic creators and builders of the Halos, which continues in Halo: Primordium. The third book in the series, Halo: Silentium is due to release in Spring 2013.
For those who missed out on its hardcover run or were waiting for it to hit trade paperback, you won't have much longer to go. I greatly enjoyed the novel (reviewed here) and I highly recommend it. If you're getting set to experience Halo 4 this November, then you'll definitely want to read both books in the series first as they flesh out a lot of essential back story.