Negative Repo Rate

On Bloomberg, Wednesday Aug 12: The repo rate on a Treasury (the 3-year note) went negative, -5bp. So, since someone shorting a Treasury is long cash and invests that cash at the repo rate, the negative rate means that this market participant will have to pay to short the note. One reason could be to reduce the number of shorts failing, i.e., to reduce the number of participants who have recently failed to deliver shorted Treasuries.

Note that, on the other side of the trade, if you use the repo market to borrow and go long a Treasury that the shorts have a hard time delivering (squeeze), you are effectively paid to borrow.