Hidden Path, the Defense Grid devs who are now so closely associated with Valve that they are working on CS:GO, have announced that Defense Grid will receive a Portal-themed called "You Monster." The expansion, which will arrive on the 7th of December, guest-stars GLaDOS as a second narrator, and sees players take on Portal-themed levels. You Monster will apparently add eight new maps for the "all new" story and thirty five challenge missions, making about fifteen hours more defending of grids.
No word on how much it's going to cost, however. $5 apparently.