Well, there was information of a surrender. In actuality, Japan had begun reaching out to the Soviets to talk of some sort of surrender. Initially, the US had been going to war against the Japanese without the Soviets because the Soviets and Japanese had signed some agreement (I forget) at the onset of the entire conflict. But Roosevelt and the USSR had quiet agreements about the USSR helping the US finish off Japan, which it was questionable if they could do alone, and agreements about stacking the deck in the USSR's favor in the Polish elections, etc. The thing is, FDR dies and Truman comes in who was not a party to any of these agreements, and at the time the US successfully tested it's nuclear technology so it no longer needed the USSR to finish off Japan. By dropping the bomb, they handled Japan without the USSR and kept Soviet influence out of the region because the surrender is then negotiated between the US and Japan and the Soviets are not a party to it. There is of course a bunch of other info that I'm not talking about, but yes, the US knew that Japan was going to fall back eventually. The means they used was just more expedient for them politically and economically (their Open Door policy).