MEMX has amended its clearly erroneous execution framework to account for overnight price protection. The SEC’s 23 October notice identifies filing SR-MEMX-2026-33 as immediately effective, while the filing says the operational change will begin with 23×5 trading, scheduled for 6 December. Filing effectiveness therefore does not mean that the overnight session is already running.[2][3]
How the review framework changes
| Trade category | Rule treatment |
|---|---|
| During overnight protected hours, 9 p.m.–4 a.m. ET | Extend the existing LULD-based restrictions on clearly erroneous reviewSource 3 |
| Trade executed within available, correct price bands | Generally stands; limited rule exceptions remainSource 3 |
| NMS stocks outside the LULD plan, such as rights and warrants | Remain eligible for review using the applicable non-regular-session numerical guidelinesSource 3 |
The filing reverses the earlier approach that treated all overnight trades like pre-market and post-market trades. It follows the SEC’s approval of overnight price bands and aims to avoid conflicting outcomes between price-band protection and subsequent trade cancellation. This does not eliminate review when the rule’s specified exceptions apply.[3]
Published 23×5 session plan — Eastern Time
| Session | Window |
|---|---|
| Overnight | 9 p.m.–4 a.m.Source 1 |
| Pre-market | 4 a.m.–9:30 a.m.Source 1 |
| Regular | 9:30 a.m.–4 p.m.Source 1 |
| Post-market | 4 p.m.–8 p.m.Source 1 |
| Daily maintenance break | 8 p.m.–9 p.m., Monday–ThursdaySource 1 |
MEMX’s FAQ makes launch conditional on approvals and readiness at DTCC, the securities information processors and listing markets. It also says outstanding orders can remain executable at 4 a.m.; members cannot assume that the overnight-to-pre-market boundary cancels them. The public target begins on Sunday evening, 6 December.[1]
Sources & further reading
- MEMX US Equities 23×5 FAQ, current as of 21 August 2026 MEMX Exchanges · Accessed 26 Oct 2026
- SEC Release 34-106727: MEMX Rule 11.15 filing US Securities and Exchange Commission · 23 Oct 2026 · Accessed 26 Oct 2026
- SR-MEMX-2026-33: amended clearly erroneous execution rules MEMX · 19 Oct 2026 · Accessed 26 Oct 2026