TBI is correct in that you cannot lock in until you are much closer to delivery. Additionally the builder likely conditioned their concessions to you're using TBI, which will pretty well lock you into their system. Moreover regarding the Jumbo conforming... all jumbo conforming loans will need to be closed by 12/1 or 12/15 or else they will not be able to be packaged as jumbo conforming - even thought eh deadline is 1/1/09, lenders won't be able to sell them to Freddie/Fannie that late. Since you are at $620K you should be fine under the new Housing Bill's $625K conforming limits. This actually works to your benefit since the interest rate for conforming is lower than the jumbo conforming rate today. Further you will find the approval process, ratios allowed etc., is automated under the conforming limits, so qualifying is easier. As for recouse in the event the rate is higher than you want... you should review your contract to see if there is a cap on the rate that would allow you out of the agreement. But keep in mind, TB wants you close on your $800K+ home, not stick you with a rediculous rate, however the rate will be determined by market conditions at the time you close. You may choose to fight them if necessary to allow you to shop outside without losing your concessions, but TB will be very resistant to this. In the end, if you still qualify even though the rate is higher, you will be required to close. TB has a reputation of wining arbitration cases and keeping deposits as well as collecting legal fees in addition, so that road is really not a wise option. In the end, they build a fine home and their mortgage company is pretty much as good as any other so you will get the best possible rate. Congratulations on your decision - you will almost certainly look back in time and conclude it was a great decision! This really is an excellent time to buy.