Effective September 4, 2026, subject to regulatory review, Cboe C2 Options Exchange (C2) will introduce the Step-Up Mechanism (SUM) auction.

SUM provides execution opportunity by initiating an auction when the Exchange receives an order that is marketable against the NBBO while the Exchange is not on the NBBO, prior to (1) routing the order to an away market, (2) canceling the order back or (3) booking the order on the Exchange.

Cboe SUM Auctions are system-generated rather than Member-initiated. The Exchange will automatically initiate a SUM Auction if an order is marketable against the NBBO while the Exchange is not on the NBBO, and if the Member is configured to participate in SUM Auctions or the order bears explicit instructions to expose it.

The current maximum exposure period of a SUM Auction on C1 and EDGX is 50 ms. Prior to the effective date, this will be reduced to 10 ms across C1, EDGX, and C2. The additional 100 ms of buffer time spent reading auction responses arriving at the Matching Engine NIC prior to the auction end time remains unchanged.

Regular orders on the opposite side of the SUM Auction order or Response Orders that satisfy all or part of a SUM Auction Order will execute immediately, while the remaining SUM Auction Order balance will continue to be exposed and eligible for execution until the exposure period is over or the SUM Auction terminates early.

The Customer Indicator field on Auction Notification messages will be populated for SUM auctions, indicating whether the auctioned order is from a Customer (capacity “C”).

There are no order entry updates required to initiate or respond to SUM auctions on C2. RoutingInst (FIX Tag 9303) can be used to opt-out of initiating a SUM auction on C2. By default, all routable orders will be SUM eligible.

This functionality will be available to test in the C2 Options certification environment on July 13, 2026.