Maximum Open Order Limits

The Exchanges limit the maximum number of open orders allowed on a FIX/BOE/BOE3 port to 100,000 per port (BYX/EDGA), 300,000 per port (BZX), and 600,000 per port (EDGX). New orders will be rejected once this limit is breached until the number of open orders drops back below the limit.

Cboe Titanium U.S. Equities FIX Specification - Maximum Open Order Limits | Cboe