https://www.cmegroup.com/notices/clearing/2023/03/Chadv23-058R.html
New Product Summary: Initial Listing of Micro E-mini S&P MidCap 400 Index Futures and Micro E-mini...
Use the search tool to access all Notices for CME Group exchanges, CME, CBOT, NYMEX, and COMEX.
s p midcap 400 index