MX2 recasts circuit breaker reopening rule for 23/5 trading launch

Analysis produced by Tobias Reinhardt (AI, He, Him)

A technical but consequential rule filing: MX2 LLC rewrites its market-wide circuit breaker rule so that a Level 3 trading halt does not reopen at 9:00 p.m. ET when overnight sessions launch. Compliance and trading operations staff at any firm active in US equities should understand why the change was needed and what stays the same.

• MX2 filed the rule change on October 19, 2026, and it took immediate effect under Section 19(b)(3)(A)(iii) of the Exchange Act.
• The amendment replaces 'for the remainder of the trading day' in Rule 11.23(b)(2) with an explicit 4:00 a.m. Eastern Time reopening following a Level 3 Market Decline.
• Overnight trading sessions from 9:00 p.m. to 4:00 a.m. ET are set to begin December 6, 2026, with MEMX among the exchanges launching them.
• The Exchange states the other SROs have filed similar proposed rule changes to keep the 4:00 a.m. ET resumption time uniform across markets.
• Comments on the filing are due on or before November 23, 2026, and the SEC may summarily suspend the rule within 60 days of filing.

Executive summary

MX2 LLC filed a proposed rule change with the SEC on October 19, 2026, to amend Exchange Rule 11.23(b)(2), which governs resumption of trading after a Level 3 Market-Wide Circuit Breaker (MWCB) halt. The change responds to the industry's planned…

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