MEMX aligns erroneous-trade rules with new overnight LULD price bands

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

This filing covers MEMX's proposed amendment to Rule 11.15 on clearly erroneous executions, prompted by the SEC's approval of Overnight Price Bands for round-the-clock trading. Compliance and trading operations staff at member firms should review the mechanics, since the change alters when a trade can be broken during overnight hours and takes effect alongside industry-wide 23/5 trading.

• MEMX filed the proposal on October 19, 2026 under File No. SR-MEMX-2026-33, effective immediately under Section 19(b)(3)(A)(iii).
• The SEC approved Overnight Price Bands via Amendment 27 to the LULD Plan on August 5, 2026 (Release No. 106042).
• The rule reverses changes MEMX made in its September 2026 23/5 Filing (SR-MEMX-2026-28) to Rule 11.15(c)(2)(A)-(D), (d)(3), and (f).
• Overnight Protected Hours are defined as 9:00 p.m. ET through 4:00 a.m. ET, with separate Overnight Percentage Parameters applying to that window.
• The change becomes operative at the start of industry-wide 23/5 trading, scheduled for December 6, 2026, with comments due by November 18, 2026.

Executive summary

MEMX LLC filed a proposed rule change with the SEC on October 19, 2026, to amend Rule 11.15, its clearly erroneous executions rule, in light of the SEC's approval of Overnight Price Bands under the LULD Plan. The filing was…

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