The IEX founder, who was the central character in the Lewis book, also defended his trading platform against critics. Asked about an IEX practice that has attracted criticism called "broker priority"—in which brokers trading on IEX can jump ahead of other traders in certain circumstances involving their own clients—Katsuyama said it is a necessary tactic to keep brokers from creating their own "dark pool" trading venues.
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"If we were the only market out there, if we had 100 percent of the volume, I could see the case against it, saying that it favors bigger brokers," Katsuyama said. "You know, I think there is a very strong case for it to stay. I think when there are 57 places to trade, you're giving people choice."
And Katsuyama continued his criticism of U.S. stock exchanges, which he said have become "economically vested" in the success of high-frequency traders over other market players.
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Katsuyama argued that the fast growth of technology—and the lucrative fees exchanges have collected from traders paying for super-fast data feeds—has pulled the exchanges away from their core business of matching buyers and sellers.
The exchanges, he said, "started selling the technology. and all of a sudden, when you're selling technology, really whether you admit it or not or whether it was intentional or not, instead of being neutral, you become economically vested in one person winning over somebody else—the person who is buying the technology."
He also said IEX has doubled its trading volume in the first quarter. IEX says its trading volume had gone from 28.4 million shares per day on average in the first quarter to 62.3 million shares per day so far in May. That has been enough, IEX said, to spark the trading venue past a number of the smaller public exchanges.
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The next hurdle for IEX will be raising capital to finance the transition to an exchange—currently it is a so-called "dark pool"—and that will require tens of millions of dollars, technological upgrades and regulatory approval.