This is true for, as you said, large hft shops. But there are thousands of quant trading firms that are not on this scale and will not be an exchange member. Yo

This is true for, as you said, large hft shops. But there are thousands of quant trading firms that are not on this scale and will not be an exchange member. You can see all the NYSE exhchange members here [0], and it's a very small portion of all quant funds. Managing margin and leverage between prime brokers is an important job for the backoffice at the fund I work for. These numbers are watched very closely, and we have strong, multiyear relationships with the people who work at these PBs. [0] https://www.nyse.com/markets/nyse-arca/membership#directory https://www.nyse.com/markets/nyse-arca/membership#directory