In less than half a day, the Federal Reserve will announce their September interest rate decision, and now everyone is speculating that they may cut interest rates by 50 basis points.

Futures trading that bets on the October federal funds rate is now extremely popular, with trading volume hitting a record high since 1988. Moreover, most of the newly opened contracts are betting that the Federal Reserve will cut by 50 basis points, and many new players have joined this week.

CME's "Fed Watch" tool also shows that now everyone believes that the possibility of a 50 basis point rate cut in September is as high as 63%.

But if the Federal Reserve only cuts by 25 basis points, instead of the 50 basis points everyone expects, the market may make a big move.