Cboe BYX amends Rule 11.29 to lock Level 3 halt resumption at 4 a.m. ET

On September 23, 2026, Cboe BYX Exchange, Inc. filed a proposed rule change (Release No. 34-106581; File No. SR-CboeBYX-2026-034; FR Doc No. 2026-20600) to amend Rule 11.29(b)(2). The notice, published October 5, 2026, states the amendment is effective immediately.

The amendment deletes the existing language that trading would halt "for the remainder of the trading day" after a Level 3 market-wide circuit breaker halt and replaces it with language specifying that trading will remain halted "until 4:00 a.m. ET or later on the following trading day." This preserves the current resumption time despite the industry's planned shift to 23/5 trading.

Under the current MWCB framework, a Level 3 Market Decline - triggered by a 20% drop in the S&P 500 Index - halts trading for the rest of the day, with the earliest possible reopening at 4:00 a.m. ET because no SROs are open before that time. The upcoming 23/5 trading sessions, slated to begin on December 6, 2026 and run from 9:00 p.m. ET to 4:00 a.m. ET, would otherwise allow an earlier restart at 9:00 p.m. ET. The Exchange, in coordination with other U.S. equity exchanges and FINRA, chose to retain the 4:00 a.m. ET resumption to maintain the cooling-off period intended by the circuit-breaker mechanism.

The Exchange asserts that the amendment is consistent with the Securities Exchange Act of 1934, specifically Section 6(b)(5), and does not alter the substantive operation of the MWCB mechanism. It is intended solely to codify the collective decision of the SROs to keep the post-Level 3 halt resumption time uniform across all trading venues.