Maximum Open Order Limits

The Exchanges limit the maximum number of open orders allowed on a FIX port to 100,000 per port (BYX/EDGA only) and 300,000 per port (BZX/EDGX only). 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