The secdef.dat file will contain CME Globex production instrument data for CME Group futures and options on futures only. It is provided as a convenience to users who have specific or unique Security Definition processing requirements. This file is static and not refreshed throughout the trading day. It should NOT be used as the primary source for Security Definition information. Best practices require that CME Globex users obtain all product information from the Reference Data API and/or Security Definition information from the MDP 3.0 channels.

This file is only updated once a day. The following intra-day changes are not reflected real-time in the Security Definition file: 

 - New products added during the day
 - Covered options strategies that expire at the end of the trading day
 - User-Defined Spreads (UDS) and User-Defined Instruments (UDI) created during the trading day.