The Hyatt has rooms for Thursday through Sunday. From what they have told us, they have sold out on Tuesday and Wednesday (there's another group at the hotel before ours, which is why rooms are tight on those nights). If you have issues booking with the online reservation system, I recommend calling the Hyatt: 425-462-1234.
We've got an overflow block at the Westin Bellevue, which is attached to the Hyatt via sky bridge, and so is very convenient. When we got the reservation code up last night, it wasn't allowing rooms booked before Wednesday June 20 and presumably after Saturday the 23th. We've asked them to add "shoulder dates" at the group rate so those coming in early or leaving later can get rooms at the group rate.
We'll be adding additional overflow rooms at nearby hotels as needed.
The hotels and registration is filling up faster than we anticipated.