This has been up for a while, at least as an ECN.
Very confusing but they seem to have a trading floor, membership, and to have done 116M or 2.2% of all US trading volume on 9/21 (ARCA, for comparison, is normally 8-10%).
If anyone has access to historic Level 2 data you should see this as IEXG. Maybe check QQQs?
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