From Tad, via his Facebook:

Jell-o brain, Night Two. Just got back from New Jersey and a story conferencing day. All good work, but it’s now three a.m. and my brain…well, you know. Wibble-wobble-wibble. However, one piece of news for the Tad readers. Shadowrise is definitely going to have to be two volumes, but only a few months apart.

And Deborah, via her Facebook:

Yes, it’s happening: Shadowrise will be 2 books, published mere months apart. So now all of Tad’s trilogies are tetralogies – ha