Before most Federal Reserve meetings, Treasury traders spend days poring over U.S. data for clues on how officials will lean. This time the bigger story is the Bank of Japan.

The BOJ has become more relevant to some U.S. traders than their own central bank as a Bloomberg survey of economists projects Gov. Haruhiko Kuroda will expand his record stimulus program Friday.

Japan's negative-interest-rate policy and bond purchases known as quantitative easing have sent most yields below zero, driving a rush for U.S. debt. The Fed will keep its benchmark rate unchanged after its meeting ends Wednesday, another survey shows.