IEX rewrites Level 3 circuit breaker rule to hold 4 a.m. reopen under 23/5 trading

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

As US exchanges prepare to extend trading to 23 hours a day, five days a week, IEX has filed a coordinated amendment to its market-wide circuit breaker rule. The change is technical but consequential: it stops the current rule text from forcing an earlier reopening after the most severe halt. Comments to the SEC are open until November 30.

• IEX amends Rule 11.271 to halt all stocks after a Level 3 MWCB until 4:00 a.m. Eastern Time or later on the following trading day.
• The change responds to 23/5 overnight trading launching on other exchanges on December 6, 2026, which would otherwise have triggered a 9:00 p.m. same-day reopen.
• IEX, the other US equity exchanges and FINRA jointly agreed to retain the existing resumption time; other SROs are expected to file parallel changes.
• The filing is designated non-controversial under Section 19(b)(3)(A) and became immediately effective, with SEC comments due by November 30, 2026.
• Level 1, Level 2 and Level 3 triggers remain at 7%, 13% and 20% single-day S&P 500 declines; the resumption time is unchanged in practice.

Executive summary

Investors Exchange (IEX) filed a proposed rule change with the SEC on November 2, 2026 to amend Rule 11.271, which governs trading halts due to extraordinary market volatility. The amendment concerns the resumption of trading after a Level 3 market-wide…

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