The interest rate remains low if there is a successful bidding and sale of these bonds.
Currently, the largest purchaser, by far, is China. They pay cash on the barrelhead.
If, for any reason, there is an unsuccessful sale, the lender of last resort, the Federal Reserve, will buy the bonds. It is done with the click of a mouse, but what effectively happens is fiat paper money is printed and put in circulation.
This act immediately begins serious inflation AND next week's bonds must carry significantly higher interest for any chance of a successful sale.
Should the Chinese decide to pass on a bond purchase, it is unlikely that any other nation or group of nations would risk taking up the slack.
Effectively, the Chinese have the power to decide if and when we go into hyper inflation and economic collapse.
Interestingly, the Chinese are no longer irresponsible utopian socialists. A significant (but falling) portion of their economy hinges on sale of Chinese manufactured goods in the US. They do not want to lose that business, but they also will not be stuck with bad debt.