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[Release No. 34-106310; File No. SR-MEMX-2026-28]

Self-Regulatory Organizations; MEMX LLC; Notice of Filing and Immediate

Effectiveness of a Proposed Rule Change to Amend its Rules to Permit Trading 23

Hours per Day, Five Days per Week

September 9, 2026.

Pursuant to Section 19(b)(1) of the Securities Exchange Act of 1934 (the “Act”), 1 and

Rule 19b-4 thereunder, 2 notice is hereby given that on August 28, 2026, MEMX LLC (“MEMX”

or the “Exchange”) filed with the Securities and Exchange Commission (the “Commission”) the

proposed rule change as described in Items I, II, and III below, which Items have been prepared

by the Exchange. The Exchange filed the proposal as a “non-controversial” proposed rule

change pursuant to Section 19(b)(3)(A)(iii) of the Act 3 and Rule 19b-4(f)(6) thereunder. 4 The

Commission is publishing this notice to solicit comments on the proposed rule change from

interested persons.

Self-Regulatory Organization’s Statement of the Terms of Substance of the Proposed

Rule Change

The Exchange is filing with the Commission a proposed rule change to amend its rules to

permit the trading of equity securities and UTP Exchange Traded Products on the Exchange 23

hours per day, five days per week. The text of the proposed rule change is provided in Exhibit 5

and is available on the Exchange’s website at https://info.memxtrading.com/regulation/rules-

15 U.S.C. 78s(b)(1).

17 CFR 240.19b-4.

15 U.S.C. 78s(b)(3)(A).

17 CFR 240.19b-4.

and-filings/.

II.

Self-Regulatory Organization’s Statement of the Purpose of, and Statutory Basis for, the

Proposed Rule Change

In its filing with the Commission, the Exchange included statements concerning the

purpose of and basis for the proposed rule change and discussed any comments it received on the

proposed rule change. The text of these statements may be examined at the places specified in

Item IV below. The Exchange has prepared summaries, set forth in sections A, B, and C below,

of the most significant aspects of such statements.

Self-Regulatory Organization’s Statement of the Purpose of, and Statutory Basis

for, the Proposed Rule Change

Purpose

The Exchange proposes to amend its rules to permit the trading of equity securities and

UTP Exchange Traded Products on the Exchange 23 hours per day, five days per week (“23x5

Trading”). The proposal is based substantially on a proposal submitted by Cboe EDGX

Exchange, Inc. (“EDGX”) that was recently approved by the Commission. 5 Further, the

Commission has approved other exchanges to offer 23x5 Trading, although none have begun to

do so. 6

See Securities Exchange Act Release No. 105587 (May 29, 2026); 91 FR 33238 (June 3, 2026) (SRCboeEDGX-2026-19) (Notice of Filing of Amendment No. 1 and Order Granting Accelerated Approval of

a Proposed Rule Change, as Amended by Amendment No. 1, To Extend the Exchange’s Trading Hours to

23 Hours per Day, Five Days per Week) (“EDGX Approval Order”). While certain of the Exchange’s rules

differ due to the Exchange’s lack of order queuing functionality, order types and modifiers, and the

Exchange’s lack of a formal opening process like EDGX, the basis for the proposal is materially similar,

and the specific sessions offered under this proposal are identical to EDGX. As such, this filing does not

raise any novel or unique issues not previously considered by the Commission.

See Securities Exchange Act Release No. 105532 (May 21, 2026); 91 FR 31509 (May 27, 2026) (SRNYSEArca-2026-53) (Notice of Filing of Filing and Immediate Effectiveness of Proposed Rule Change To

Amend Temporary Rule 7.34-E(T) To Provide for an Overnight Trading Session and To Amend the Hours

for the Exchange’s Early Trading Session and the Late Trading Session, and To Make Corresponding

Changes to Other Rules); Securities Exchange Act Release No. 890235 [sic] (November 27, 2024); 89 FR

97072 [sic] (Order Approving Application of 24X National Exchange, LLC for registration as a national

securities exchange and to trade 23 hours per day, 5 days per week) (“24X Approval Order”); Securities

Background

The latest change to impact the markets is rising investor interest in trading U.S. equities

during overnight hours, especially among investors located outside of the United States. To align

MEMX with emerging investor interest in trading outside of traditional U.S. Market hours, the

Exchange proposes to extend its hours for trading to 23 hours per day, 5 days per week. The

Exchange believes that 23x5 Trading will benefit investors and the national market system by

increasing market accessibility, promoting capital formation, and facilitating portfolio

management.

Currently, Users 7 may enter orders into the System 8 from 4:00 a.m. to 8:00 p.m. Eastern

Time (“ET”). 9 The Exchange offers three trading sessions on each day it is open for trading: (1)

the Pre-Market Session 10 (4:00 a.m. to 9:30 a.m.); (2) Regular Trading Hours 11 (9:30 a.m. to

4:00 p.m.); and (3) the Post-Market Session 12 (4:00 p.m. to 8:00 p.m.). During each session,

orders may be entered, executed, or routed away. 13 The Exchange does not offer queueing

functionality, and as such, it does not accept orders prior to any trading session, however, it only

Exchange Act Release No. 105199 (April 10, 2026); 91 FR 20222 (April 15, 2026) (SR-Nasdaq-2025-109)

(Notice of Filing of Amendment Nos. 2 and 3 and Order Granting Accelerated Approval of a Proposed

Rule Change, as Amended by Amendment Nos 2 and 3, To Extend the Exchanges’ Trading Hours to 23

Hours a Day, Five Days a Week) (“Nasdaq Approval Order”).

The term “User” shall mean any Member or Sponsored Participant who is authorized to obtain access to the

System pursuant to Rule 11.3[sic] See Rule 1.5(jj).

The term “System” shall mean the electronic communications and trading facility designated by the Board

through which securities orders of Users are consolidated for ranking, execution and, when applicable,

routing. See Rule 1.5(gg).

See Rule 11.1(a). All times stated herein are in ET.

See Rule 1.5(x).

See Rule 1.5(bb). “Regular Trading Hours” is also referred to in the Exchange’s rules as the “Market

Session” which is defined in Rule 1.5(o).

See Rule 1.5(w).

See Rule 11.1(a).

accepts certain order types during specific sessions. For example, Market Orders 14 are only

eligible for execution by the System during the Market Session, 15 and not during the Pre-Market

or Post-Market Sessions.

To accommodate 23x5 Trading, the Exchange proposes to introduce a new Overnight

Trading Session, along with conforming amendments to its session-specific order handling rules,

as described below.

Proposal

The Exchange proposes to amend its rules to enable 23x5 Trading by adopting a new

Overnight Trading Session.

Definitions

The Exchange proposes to amend and adopt certain definitions provided in Exchange

Rule 1.5.

First, the Exchange proposes to adopt the new defined term, “Overnight Trading

Session.” As proposed, the Overnight Trading Session shall mean the time between 9:00 p.m. on

any night preceding a business day 16 and 4:00 a.m. on the following calendar day. Rather than

defining the Overnight Trading Session by reference to specific calendar days of the week (e.g.,

Sunday through Thursday), the proposed definition is anchored to the concept of a “night

preceding a business day.” This approach provides that the Overnight Trading Session is

triggered by the existence of an upcoming trading day rather than by enumeration of calendar

days, providing a more durable and flexible framework that accommodates changes to the

“Market Orders” are orders to buy or sell a stated amount of a security that is to be executed at the NBBO

or better when the order reaches the Exchange. See Rule 11.8(a).

See Rule 11.8(a)(4).

See proposed Rule 11.1(b). A business day is any day the Exchange is open for trading, which includes any

Monday, Tuesday, Wednesday, Thursday, and Friday, other than a holiday.

Exchange’s trading calendar (including holidays and other non-business days) without requiring

conforming amendments to the session definition itself. For example, when a holiday falls on a

Monday, there is no night preceding a business day on the prior Sunday and therefore no

Overnight Trading Session will commence that Sunday evening, consistent with the Exchange’s

proposed holiday schedule under Rule 11.1(b). As discussed further below under “Contingency

on Industry Readiness,” the Exchange shall not commence operation of the Overnight Trading

Session until specified Equity Data Plan readiness conditions have been satisfied. The proposed

term would provide “Overnight Trading Session” shall mean the time between 9:00 p.m. on any

night preceding a business day, as provided in Rule 11.1(b), and 4:00 a.m. Eastern Time on the

following calendar day. For the avoidance of doubt, notwithstanding anything to the contrary in

these Rules, the Exchange shall not commence operation of the Overnight Trading Session

unless the Equity Data Plans (1) have established a mechanism to collect, consolidate, process

and disseminate quotation and transaction information at all times during the Overnight Trading

Session that is equivalent to the mechanism established for Exchange trading hours during

Regular Trading Hours, and (2) have provided the Exchange with notification that they are

prepared to collect, consolidate, process and disseminate quotation and transaction information

to accommodate the Overnight Trading Session. Prior to commencing operation during the

Overnight Trading Session, the Exchange will file a proposed rule change pursuant to Section

19(b) of the Exchange Act and the rules thereunder to amend its rules confirming that the

Exchange is able to comply with its obligations under the Exchange Act and the rules thereunder

during the Overnight Trading Session and that such Equity Data Plans are prepared to collect,

consolidate, process and disseminate quotation and transaction information at all times during

the Overnight Trading Session (“Overnight Trading Session Proposed Rule Change”). If the

Overnight Trading Session Proposed Rule Change is not filed within 18 months of the

effectiveness of this proposed rule change, the Exchange will promptly file a proposed rule

change to remove the rules that apply to the Overnight Trading Session.

Second, proposed Rule 1.5(i) would define “Equity Data Plans” to mean the effective

national market system plan(s) governing the collection, consolidation, processing, and

dissemination of consolidated equity market data via the exclusive securities information

processors (“SIPs”), including: (1) the Consolidated Tape Association Plan (“CTA Plan”); (2)

the Consolidated Quotation Plan (“CQ Plan”); (3) the Joint Self-Regulatory Organization Plan

Governing the Collection, Consolidation and Dissemination of Quotation and Transaction

Information for Nasdaq-Listed Securities Traded on Exchanges on an Unlisted Trading

Privileges Basis (“UTP Plan”); (4) the CT Plan established by the Limited Liability Company

Agreement of CT Plan LLC; and (5) any successor to the named Plan(s).

Trading Rules

The Exchange proposes to amend Rules 11.1 (Hours of Trading and Trading Days), 11.6

(Definitions), 11.8 (Order Types and Modifiers), 11.10 (Order Execution), 11.15 (Clearly

Erroneous Executions), 11.22 (Limit Up-Limit Down Plan and Trading Halts on the Exchange),

and to adopt Rule 11.24 (Weekday Trading Pauses) to reflect necessary updates to provide for

23x5 trading functionality.

a. Rule 11.1 – Hours of Trading and Trading Days

The Exchange proposes to amend Rule 11.1(a) to add reference to the Overnight Trading

Session, and to adopt Rule 11.1(a)(1) to establish session eligibility framework to accommodate

23x5 Trading. Under current Rule 11.1(a), orders may be entered, canceled, modified, executed

on, or routed away from the Exchange during the Pre-Market Session, the Market Session, 17 and

the Post-Market Session. The current rule also provides that all orders are eligible for execution

during the Market Session, and that orders may be entered into the System during Exchange

Operating Hours (from 4:00 a.m. until 8:00 p.m. Eastern Time).

The Exchange proposes to add the Overnight Trading Session to the list of sessions in

which orders may be entered, canceled, modified, executed on or routed away from the

Exchange, and indicate that orders may be entered into the System starting at 9:00 p.m. Eastern

Time on any day preceding a business day, as provided in Rule 11.1(b), until 8:00 p.m. Eastern

Time on the same trading day. 18

Proposed Rule 11.1(a)(1) would provide that an order is eligible to participate in the

designated trading session(s) only and may remain in effect for one or more consecutive trading

sessions on a particular day. An order designated for a session that has not yet begun or has

already ended will be rejected. An order entered without a trading session designation will

default to a Day 19 order, making it eligible to participate from the Overnight Trading Session

through the end of Regular Trading Hours.

The Exchange also proposes to amend Rule 11.1(b) to define “business day” and to

specify the days on which the Exchange will be open for trading under the proposed 23x5

framework. A business day is any day the Exchange is open for trading, which includes any

Monday, Tuesday, Wednesday, Thursday, and Friday, other than a holiday listed below. The

See supra note 11.

A “trading day” refers to the 23-hour period commencing at 9:00 p.m. ET on one calendar day and ending

at 8:00 p.m. ET on the next calendar day for the period from Sunday at 9:00 p.m. ET through Friday at 8:00

p.m. ET.

A “Day” order is defined under the proposed amended Rule 11.6(o)(2) as an instruction the User may

attach to an order stating that an order to buy or sell starting with the Overnight Trading Session and, if not

executed, expires at the end of Regular Trading Hours.

Exchange will not be open for business on the following holidays: New Year’s Day, Dr. Martin

Luther King Jr. Day, Presidents’ Day, Good Friday, Memorial Day, Juneteenth National

Independence Day, Independence Day, Labor Day, Thanksgiving Day, and Christmas Day.

When a holiday falls on a Saturday, the Exchange will not be open for business on the preceding

Friday. When a holiday falls on a Sunday, the Exchange will not be open for business on the

following Monday, unless otherwise indicated by the Exchange. On days when the Exchange

closes early (“Early Market Close”), Regular Trading Hours will be from 9:30 a.m. to 1:00 p.m.

and the Post-Market Session will be from 1:00 p.m. to 5:00 p.m. Trading shall resume with the

Overnight Trading Session on any night preceding a business day. The Exchange also proposes

to amend Rule 11.1(b) to provide that the Exchange will be open for the transaction of business

on each business day, including the Overnight Trading Session on the preceding calendar day.

Under the proposed 23x5 framework, the trading day will be structured as follows. The

Overnight Trading Session will run from 9:00 p.m. to 4:00 a.m., followed by the Pre-Market

Session from 4:00 a.m. to 9:30 a.m., Regular Trading Hours from 9:30 a.m. to 4:00 p.m., and the

Post-Market Session from 4:00 p.m. to 8:00 p.m. Between 8:00 p.m. and 9:00 p.m. each

weekday, the Exchange will pause trading to conduct maintenance, testing, and processing of

corporate actions (such as mergers, stock splits, and dividends) that become effective the

following trading day. 20 This pause also provides market participants with time to process and

clear trades before the start of a new trading day. For dates on which the Exchange is not open

for business under Rule 11.1(b), the market closure will be effective at 8:00 p.m. on the calendar

As noted above, these trading sessions are identical to those in the EDGX Approval Order, other than the

titles given to the Pre-Market and Post-Market Sessions, which are known as the Pre-Opening and PostClosing Sessions on EDGX.

day preceding the closure date. For Early Market Close days, 21 the closure will instead be

effective at 5:00 p.m. on the calendar day preceding the closure date. In either case, the

Exchange will re-open at 9:00 p.m. on the closure date, unless the closure date is immediately

followed by a non-business day, in which case the Exchange will re-open at 9:00 p.m. on the day

preceding the next business day.

b. Rule 11.6(o) – Time-In-Force “TIF” Instructions

The Exchange does not propose any changes to its existing TIF instructions in connection

with the Overnight Trading Session, with two exceptions described below. The Exchange

believes the existing TIF framework otherwise accommodates the proposed 23x5 structure

without modification.

The Exchange proposes a conforming amendment to the Day order TIF definition to

permit acceptance of Day Orders during the Overnight Trading Session. Under the current

definition, a Day Order entered “into the System before the opening for business on the

Exchange as determined pursuant to Rule 11.1, or after the closing of Regular Trading Hours” is

rejected. Because the Overnight Trading Session commences at 9:00 p.m. the current definition

would, as written, result in the rejection of Day Orders entered during the Overnight Trading

Session. This outcome is inconsistent with the proposed 23x5 framework, under which Day

Orders should be eligible for entry beginning at the Overnight Trading Session and should

remain eligible for execution throughout the Overnight Trading Session, Pre-Market Session,

and Regular Trading Hours. Accordingly, the Exchange proposes to amend the Day order TIF

definition to provide that a Day Order entered during the Overnight Trading Session will be

Regular trading hours for days when the market closes early are typically 9:30 a.m. to 1:00 p.m. See e.g.,

Thanksgiving Early Close and Christmas Early Close at: https://info.memxtrading.com/market-hours-andholiday-schedule/[sic]

accepted by the Exchange and, if not executed, will expire at the end of Regular Trading Hours

on the same trading day. For added clarity, the Exchange also proposes to add that any Day

Order entered into the System during the Post-Market Session or before the opening for business

on the Exchange as determined pursuant to Rule 11.1 will be rejected.

This amendment is limited to conforming the Day order definition to the expanded order

entry window introduced by the proposed 23x5 framework and does not alter any other aspect of

the Day order TIF instruction. For the avoidance of doubt, orders will expire on the trading day

for which they are entered; as described above, a trading day is deemed to begin at 9:00 p.m.

Eastern Time on the preceding calendar day. As amended, a Day Order entered at 9:00 p.m. on a

day preceding a business day will remain eligible for execution throughout the Overnight

Trading Session, Pre-Market Session, and Regular Trading Hours on that business day, expiring

at 4:00 p.m. Eastern Time that trading day.

Second, the Exchange is proposing a conforming amendment to the definition of the TIF

“Good-’til Time (“GTT”) in order to permit acceptance of GTT Orders during the Overnight

Trading Session. Currently, GTT is a TIF the User may attach to an order specifying the time of

day at which the order expires, which is designated for execution starting with the Pre-Market

Session. Any unexecuted portion of an order with a TIF instruction of GTT will be cancelled at

the expiration of the User’s specified time, which can be no later than the close of the PostMarket Session. At this time, the Exchange proposes to replace the reference to the “Pre-Market

Session” with the “Overnight Trading Session”, as the intent of the 23x5 framework is to begin

the business day with the Overnight Trading Session, rather than the Pre-Market Session. This

amendment is limited to conforming the GTT order definition to the expanded order entry

window introduced by the proposed 23x5 framework and does not alter any other aspect of the

GTT order instruction.

c. Rule 11.8 – Order Types

The Exchange proposes two conforming amendments to Rule 11.8 to add reference to the

Overnight Trading Session in the two order types that currently specify session eligibility, Limit

Orders 22 and Pegged Orders. 23 Specifically, both of these order types are currently eligible for

execution during the Pre-Market Session, Market Session, and Post-Market Session, and the

Exchange proposes to add the Overnight Trading Session to this list in order to ensure that those

orders are permitted in all offered sessions. However, the Exchange proposes additional

amendments with respect to Pegged Orders.

As noted previously, Pegged Orders are currently eligible for execution during the PreMarket Session, Market Session, and Post-Market Session, and per Rule 11.6(h)(1) and (2), a

User may, but is not required to, include a limit price on Pegged Orders. The Exchange is now

proposing to amend Rule 11.8(c)(4) to require that any Pegged Orders entered outside of Regular

Trading Hours must be entered with a limit price. Specifically, the Exchange’s proposed text

indicates all Pegged Orders may be entered during the Market Session, and only Pegged Orders

with a limit price may be entered during the Overnight Trading Session, Pre-Market Session, and

the Post-Market Session. 24 As a result of this change, Pegged Orders entered without a limit

price will be rejected during the Overnight Trading Session, Pre-Market Session, and PostMarket Session. The Exchange wishes to make this change given that Pegged Orders without

limit prices represent heightened execution risk in extended hours sessions where liquidity

See Rule 11.8(b).

See Rule 11.8(c).

The Exchange is proposing to delete the word “executed” in this provision (Rule 11.8(c)(4)), and replace it

with the word “entered” for the purpose of added clarity.

conditions may differ materially from those present during Regular Trading Hours and where the

NBBO may be wider or less reliable. Without a limit price to constrain the execution price, a

Pegged Order could execute at a price that is disadvantageous to the submitting party in a

manner that is less likely to occur during Regular Trading Hours, due to the potential lack of

liquidity and less reliable NBBO. The Exchange notes that this amendment is consistent with

EDGX, where orders without a limit price are similarly prevented from executing outside of

Regular Trading Hours.

d. Rule 11.10 – Order Execution

The Exchange proposes a conforming amendment to Rule 11.10 to reference the

Overnight Trading Session in the provision governing compliance with Regulation NMS. As

amended, for any execution to occur during the Overnight Trading Session, Pre-Market Session,

or Post-Market Session, the price must be equal to or better than the highest bid or lowest offer

in the MEMX Book or as disseminated by the responsible single plan processor, unless the order

is marked ISO or a Protected Bid is crossing a Protected Offer. This amendment is nonsubstantive and preserves the existing execution standard applicable outside of Regular Trading

Hours.

Additionally, to support 23x5 trading, the Exchange will offer Members a risk control

under Rule 11.10, Interpretation and Policy .01(c) that would prohibit orders from executing

during the Overnight Trading Session. The Exchange plans to offer this new control as one of the

controls available to Members under this provision, which permits the Exchange to offer

“controls related to the order types or modifiers that can be utilized (including pre-market, postmarket, short sales and ISOs)”. Accordingly, the Exchange proposes to add the word “overnight”

to the parenthetical in Rule 11.10, Interpretation and Policy .01(c). 25

e. Rule 11.15 – Clearly Erroneous Executions

The Exchange proposes conforming amendments to Rule 11.15 to add references to the

Overnight Trading Session throughout the clearly erroneous execution framework. These

amendments appear in the provisions governing review of transactions occurring outside of

Regular Trading Hours, including the numerical guidelines table, the Multi-Stock Event

provisions, the additional factors provision, the Outlier Transaction provision, the Reference

Price provision, and the Officer Acting On Own Motion provision. In each case, the amendment

adds “Overnight Trading Session” alongside “Pre-Market Session” and “Post-Market Session”

without altering the substantive standards or procedures applicable to clearly erroneous

execution reviews. The Exchange notes that the numerical guidelines applicable to the Overnight

Trading Session, Pre-Market Session, and Post-Market Session will remain the same as those

currently applicable to the Pre-Market Session, and Post-Market Session, reflecting the

Exchange’s view that the same heightened thresholds appropriate for extended hours trading

remain appropriate for the Overnight Trading Session.

f. Rule 11.24 – Weekday Trading Pause

The Exchange proposes to adopt new Rule 11.24 to govern the daily trading pause that

will occur between the close of the Post-Market Session and the commencement of the

Overnight Trading Session on each weekday. As proposed, the Exchange will pause trading at

the conclusion of the Post-Market Session at 8:00 p.m. and resume trading with the

commencement of the Overnight Trading Session at 9:00 p.m. on the day preceding the next

The Exchange is also proposing a non-substantive amendment to Rule 11.10, Interpretation and Policy

.01(c) to correct a typographical error, adding an inadvertently omitted hyphen in “pre-market”.

business day. This one-hour pause is intended to provide the Exchange with time to conduct

necessary maintenance and testing, and to process corporate actions, such as mergers, stock

splits, and dividends, that become effective the following trading day.

The pause also provides market participants with time to process and clear trades before

the start of a new trading day. Proposed Rule 11.24(a)(1) provides that all orders outstanding on

the MEMX Book as of 8:00 p.m. at the end of the Post-Market Session will be cancelled. The

Exchange believes it is appropriate to cancel all resting orders at the close of the Post-Market

Session each weekday to ensure that orders are not carried over into the next trading day without

an explicit order instruction by a Member. This approach provides Members with a clean start to

each trading day and reduces the risk of unintended executions based on stale order instructions.

Proposed Rule 11.24(a)(2) provides that the Exchange will begin accepting orders again

at the commencement of the Overnight Trading Session at 9:00 p.m. Eastern Time and continue

until 8:00 p.m. the following calendar day, provided the next calendar day is not a holiday or a

Friday. Proposed Rule 11.24(a)(2) also provides that trades occurring at or after the

commencement of the Overnight Trading Session at 9:00 p.m. will be assigned a trade date of

the following day, reflecting that the Overnight Trading Session economically belongs to the

next trading day even though it commences the prior evening.

Unlisted Trading Privileges

The Exchange proposes conforming amendments to Rule 11.22 to insert references to the

Overnight Trading Session with the Pre-Market Session. These amendments are non-substantive

and are intended solely to conform the unlisted trading privileges framework to the proposed

23x5 session structure by updating the applicable session nomenclature and hours.

Risk Disclosures

The Exchange proposes to adopt new Rule 3.21(h) to establish tailored customer

disclosure obligations specific to the Overnight Trading Session and Pre-Market Session. The

existing customer disclosure framework under Rule 3.21 requires Members to disclose the

material trading risks associated with extended hours trading prior to accepting an order for

execution in those sessions. 26 The Exchange believes that the unique characteristics of the

Overnight Trading Session and Pre-Market Session (including the hours during which they

operate, the market conditions that may be present, and the novel nature of overnight exchange

trading) warrant additional disclosures beyond those currently required for other extended hours

sessions. Proposed Rule 3.21(h) sets forth seven categories of risks that Members must disclose

to customers in connection with trading during the Overnight Trading Session and Pre-Market

Session.

First, proposed Rule 3.21(h)(1) addresses the risk of trading during hours in which

primary listing markets may not be open. Unlike the Post-Market Session, which occurs in close

proximity to Regular Trading Hours, the Overnight Trading Session and Pre-Market Session

operate during hours in which primary listing exchanges may not be conducting their own

trading, regulatory surveillance, or other regulatory functions with respect to their listed

securities. The Exchange believes it is important that customers understand that the regulatory

infrastructure ordinarily provided by primary listing exchanges may not be available during these

sessions.

Second, proposed Rule 3.21(h)(2) addresses the risk that regulatory protections available

The Exchange is proposing to make a minor, non-substantive amendment to Rule 3.21 to change “UTP

Derivative Securities as defined in Rule 14.1(c)” to “UTP Exchange Traded Products as defined in Rule

1.5(kk)”.

during the Overnight Trading Session and Pre-Market Session may be more limited or different

than those available during Regular Trading Hours. For example, certain volatility control

mechanisms applicable to individual symbols and the broader equities market may not be

available during the Overnight Trading Session and Pre-Market Session. The Exchange believes

customers should be informed of these potential gaps in regulatory protections before trading

during these sessions.

Third, proposed Rule 3.21(h)(3) addresses the risk arising from limited trading

alternatives during the Overnight Trading Session and Pre-Market Session. Because the

Exchange may be the only exchange trading certain securities during these hours, customers may

face greater exposure to losses in the event of systems failures or other operational issues on the

Exchange, as alternative execution venues may not be available.

Fourth, proposed Rule 3.21(h)(4) addresses the risks associated with near- continuous

trading under the 23x5 framework. With the implementation of the Overnight Trading Session,

trading on the Exchange will occur on a near-continuous basis throughout the week, with only

limited breaks. This structure may present heightened risks related to system maintenance and

testing, as well as the pausing and resumption of trading, as there will be fewer extended breaks

during which such activities can be conducted without impacting market participants.

Fifth, proposed Rule 3.21(h)(5) addresses the risk of trading during hours in which

financial market infrastructure companies are closed. Certain important financial market

infrastructure providers, including other markets, banks, Fedwire Funds Service, and certain

other providers of settlement services, may be closed during the Overnight Trading Session and

Pre-Market Session. Trading during hours in which the relevant clearing agency and other

settlement service providers are closed may result in an increased passage of time between the

execution of a transaction and its final settlement, which may expose customers to additional

counterparty and settlement risk.

Sixth, proposed Rule 3.21(h)(6) addresses the risk arising from the novel nature of

overnight exchange trading. Exchange-facilitated trading during overnight hours is a relatively

new development in the U.S. equities market, and as such, the Overnight Trading Session may

present unforeseen risks that are not yet fully understood or anticipated. The Exchange believes

it is appropriate to specifically call out the novelty of the Overnight Trading Session so that

customers can make informed decisions about whether overnight trading is appropriate for them.

Seventh, proposed Rule 3.21(h)(7) provides a general catch-all disclosure acknowledging

that the Overnight Trading Session and Pre-Market Session may present additional unforeseen

risks beyond those specifically enumerated in proposed Rule 3.21(h)(1) through (6). The

Exchange believes this provision is appropriate given the evolving nature of extended hours

trading and the potential for market conditions or operational circumstances that cannot be fully

anticipated at this time.

The Exchange believes that the proposed disclosures under Rule 3.21(h) are necessary

and appropriate to ensure that customers are fully informed of the unique risks presented by the

Overnight Trading Session and Pre-Market Session prior to participating in trading during those

hours. The proposed disclosures are consistent with the customer protection principles

underlying the existing Rule 3.21 framework and reflect the Exchange’s commitment to investor

protection in connection with the expansion of its trading hours under the proposed 23x5

framework.

Protections

The implementation of 23x5 Trading represents an extension of trading hours rather than

a fundamental restructuring of Exchange operations or rules. With the exception of the specific

amendments discussed above, the Exchange’s operational processes, rule text, and surveillance

programs will continue to apply in the same manner as they do today. The following MEMX

rules and system features will remain unchanged and will apply in full during the Overnight

Trading Session: Order Types and Order Execution; Membership Rules and Rules of Fair

Practice; Market Maker Obligations and Priority of Orders; Trading Practice Rules and

Disciplinary Rules and Enforcement; Clearly Erroneous Execution Protections; and Risk

Settings.

With respect to trading halts, the Exchange’s existing halt rules will apply during the

Overnight Trading Session. Consistent with current practice during other extended hours

sessions, the Exchange will halt trading in a security during the Overnight Trading Session to the

extent required to follow a halt imposed by the primary listing exchange for that security. To the

extent a security is subject to a regulatory halt, news dissemination halt, or other trading pause

imposed by the primary listing exchange or a national securities regulator, the Exchange will halt

trading in that security consistent with applicable rules and regulatory requirements.

The Exchange’s clearly erroneous execution rules under Rule 11.15 will apply in full

during the Overnight Trading Session, as they currently apply during the Pre-Market Session and

other extended hours sessions. No substantive changes to those rules are proposed in connection

with this filing. As such, the Exchange’s Clearly Erroneous rules will continue to mirror those

adopted by each national security exchange and will continue to ensure that there are consistent

standards across each exchange for breaking trades, and continuing to promote the orderly and

efficient operation of the equities markets.

The Exchange’s existing surveillance programs and compliance infrastructure will

likewise apply fully to trading in the Overnight Trading Session. The Exchange currently

operates a comprehensive regulatory program applicable to the Pre-Market Session, Regular

Trading Hours, and Post-Market Session, encompassing a suite of automated trade surveillance

tools, routine Member examinations, and an exam-based regulatory program. This regulatory

program will extend to the Overnight Trading Session without modification, ensuring that

Members trading during overnight hours are subject to the same level of oversight applicable to

trading in other sessions. Similarly, the Exchange’s existing risk settings and controls (including

single order price and size protections and other fat finger safeguards) will remain available and

operative during the Overnight Trading Session. The Exchange believes that these existing

protections, taken together, provide a robust framework for managing risk during overnight

trading that is consistent with the protections available during other extended hours sessions.

Contingency on Industry Readiness

As noted above, the Exchange will not implement its proposed rule changes or

commence operation of the Overnight Trading Session until the Equity Data Plan readiness

conditions set forth in proposed Rule 1.5(i) have been satisfied. Prior to commencing operation

of the Overnight Trading Session, the Exchange will file a proposed rule change pursuant to

Section 19(b) of the Exchange Act and the rules thereunder confirming that: (i) the Exchange is

able to comply with its obligations under the Exchange Act and the rules thereunder during the

Overnight Trading Session; and (ii) the Equity Data Plans are prepared to collect, consolidate,

process, and disseminate quotation and transaction information at all times during the Overnight

Trading Session. Upon satisfaction of the foregoing conditions, the Exchange will announce via

Trader Alert the implementation date for its proposed rule changes and the go-live date for 23x5

Trading. If the Overnight Trading Session Proposed Rule Change is not filed within 18 months

of the effectiveness of this proposed rule change, the Exchange will promptly file a proposed rule

change to remove the rules applicable to the Overnight Trading Session.

Impact on Fees

Any impact of the Exchange’s 23x5 proposal on its fee schedule will be addressed in a

subsequent fee filing.

Statutory Basis

The Exchange believes the proposed rule change is consistent with the Securities

Exchange Act of 1934 (the “Act”) and the rules and regulations thereunder applicable to the

Exchange and, in particular, the requirements of Section 6(b) of the Act. 27 Specifically, the

Exchange believes the proposed rule change is consistent with the Section 6(b)(5) 28 requirements

that the rules of an exchange be designed to prevent fraudulent and manipulative acts and

practices, to promote just and equitable principles of trade, to foster cooperation and

coordination with persons engaged in regulating, clearing, settling, processing information with

respect to, and facilitating transactions in securities, to remove impediments to and perfect the

mechanism of a free and open market and a national market system, and, in general, to protect

investors and the public interest.

23x5 Trading Framework

The Exchange believes the proposed rule change is consistent with the Act because it

would remove impediments to and perfect the mechanism of a free and open market and a

national market system by providing a rules framework to support 23x5 Trading. As described

above, the Exchange believes that 23x5 Trading will benefit investors and the national market

15 U.S.C. 78f(b).

15 U.S.C. 78f(b)(5).

system by increasing market accessibility, promoting capital formation, and facilitating portfolio

management, including for the growing number of retail investors outside of the United States

whose local business hours do not coincide with U.S. Regular Trading Hours.

The Exchange further believes the proposal is consistent with the Act because the

proposed Overnight Trading Session will operate in substantially the same manner as the

Exchange’s existing extended hours sessions. All order types, execution processes, membership

rules, market maker obligations, priority rules, disciplinary rules, clearly erroneous execution

protections, risk settings, and fat finger safeguards applicable to the Exchange’s existing sessions

will continue to apply in full during the Overnight Trading Session. The Exchange believes that

applying its existing operational and regulatory framework to the Overnight Trading Session is

consistent with the Act’s goals of ensuring market integrity, investor protection, and fair and

orderly trading. The Exchange represents that its systems have the capacity to accommodate the

proposed 23x5 Trading functionality.

Session Definitions and Order Entry Framework

The Exchange believes that the proposed new definitions, including the Overnight

Trading Session and Equity Data Plans, would remove impediments to and perfect the

mechanism of a free and open market and a national market system by adding clarity and

transparency to the Exchange’s rules. The proposed Overnight Trading Session definition,

anchored to the concept of a “night preceding a business day” rather than enumerated calendar

days, provides a durable and flexible framework that accommodates the Exchange’s trading

calendar without requiring recurring conforming amendments. The Exchange believes these

definitional additions facilitate the understanding of and compliance with Exchange rules,

thereby removing potential confusion and promoting just and equitable principles of trade.

The Exchange believes the proposed streamlined order entry framework under Rule

11.1(a) similarly removes impediments to the mechanism of a free and open market by adding

the Overnight Trading Session to the fulsome list of trading sessions offered by the Exchange

during which orders may be entered, canceled, modified, executed on or routed away from the

Exchange, and replacing the Exchange’s current operating hours with the new operating hours

which include the Overnight Trading Session. The proposed trading session designation

requirement under Rule 11.1(a)(1) promotes transparency and investor protection by ensuring

that each order is clearly designated for the session(s) in which it will remain eligible to

participate, consistent with the approach taken by other national securities exchanges that have

adopted or sought to adopt extended overnight trading frameworks. 29

The Exchange believes that the proposed introduction of a defined term “business day” in

Rule 11.1(b), together with the codification of the concept of an Early Market Close and the

corresponding adjustments to the Exchange’s trading calendar, is consistent with Section 6(b)(5)

of the Act because these amendments remove impediments to and perfect the mechanism of a

free and open market and a national market system. As proposed, a “business day” is any day the

Exchange is open for trading, each Monday through Friday that is not a holiday, thereby

providing a clear and predictable foundation for determining when the Overnight Trading

Session will operate. This definition, which does not rely on enumerated calendar days, enhances

transparency and flexibility by ensuring that the commencement of the Overnight Trading

Session is tied to whether the following day is a trading day rather than to fixed days of the

week. The proposed amendment also provides that the Exchange will be open for the transaction

of business on each business day, including the Overnight Trading Session on the preceding

See supra notes 5 and 6.

calendar day, thereby confirming the full scope of Exchange operations under the 23x5

framework and providing Members with a clear and comprehensive statement of when the

Exchange is open. This structure accommodates holiday closures, holiday-observed weekends,

and unforeseen non-business days without requiring further amendments to the session

definition. Likewise, the proposal’s integration of Early Market Close days (under which Regular

Trading Hours conclude at 1:00 p.m. and the Post-Market Session ends at 5:00 p.m., with the

market closure becoming effective on the calendar day preceding the closure date) provides that

the transition into the Overnight Trading Session remains orderly, predictable, and aligned with

the modified market-wide trading schedule. Together, these provisions provide Members with a

uniform, rules-based mechanism for determining when the Exchange will commence and pause

trading under the proposed 23x5 framework, promote just and equitable principles of trade by

reducing uncertainty and the risk of misaligned order entry during session transitions, and foster

cooperation and coordination with other market participants and infrastructure providers by

grounding the Overnight Trading Session in a clear and durable trading-day framework.

Accordingly, the Exchange believes the proposed amendments are consistent with the protection

of investors and the public interest because they provide predictable and transparent operational

parameters for the launch and operation of the Overnight Trading Session.

Contingency on Equity Data Plan Readiness

The Exchange believes that conditioning commencement of the Overnight Trading

Session on satisfaction of the Equity Data Plan readiness requirements set forth in proposed Rule

1.5(i) is consistent with the Act and, in particular, with the Act’s requirements that exchange

rules be designed to prevent fraudulent and manipulative acts and practices, foster cooperation

and coordination with persons engaged in regulating, clearing, settling, and processing

information with respect to securities transactions, and perfect the mechanism of a free and open

market and a national market system. As the Commission has recognized in approving similar

conditions for other exchanges seeking to operate overnight sessions, this requirement is

designed to reasonably ensure that consolidated quotation and transaction data are provided in a

manner consistent with existing extended hours sessions, and that trading will not occur until the

infrastructure necessary to support fair and orderly markets during overnight hours is in place. 30

Prior to commencing operation of the Overnight Trading Session, the Exchange will confirm via

a subsequent Section 19(b) filing that the Equity Data Plans are prepared to collect, consolidate,

process, and disseminate quotation and transaction information at all times during the Overnight

Trading Session and that the Exchange is able to comply with its obligations under the Act

during those hours. The Exchange believes this approach promotes transparency because trading

will not commence until these conditions are verified and publicly filed.

Order Type Eligibility

The Exchange believes the proposed conforming amendments to its Limit Order and

Pegged Order order type rules are consistent with the Act because they include the Overnight

Trading Session in addition to the Pre-Market, Market, and Post-Market Sessions, thereby

ensuring a consistent and investor-protective trading environment across all extended hours

sessions.

Weekday Trading Pause

The Exchange believes the proposed Weekday Trading Pause under new Rule 11.24 is

consistent with the Act because it promotes the protection of investors and the public interest by

providing the Exchange and market participants with a defined period each weekday to conduct

Id.

maintenance and testing, process pending corporate actions, and clear end-of-day positions

before a new trading day commences. The cancellation of all resting orders at the end of the

Post-Market Session at 8:00 p.m. each weekday promotes investor protection by ensuring that

Members must affirmatively re-enter orders for the following trading day, reducing the risk of

unintended executions based on stale order instructions.

Customer Disclosures

The Exchange believes proposed Rule 3.21(h) is consistent with the Act and, in

particular, with the Section 6(b)(5) requirement that exchange rules be designed to promote just

and equitable principles of trade, remove impediments to and perfect the mechanism of a free

and open market and a national market system, and protect investors and the public interest. The

seven categories of risk disclosure required by proposed Rule 3.21(h) (addressing the absence of

primary listing market oversight during overnight hours, the potential for more limited regulatory

protections, limited trading alternatives, risks associated with near-continuous trading, the

closure of financial market infrastructure companies during overnight hours, the novel nature of

overnight exchange trading, and potential unforeseen risks) are tailored to the specific

characteristics of the Overnight Trading Session and the Pre-Market Session, and are

substantially similar to the disclosures required by the Commission in approving the rules of

other national securities exchanges operating on an extended overnight basis. 31 The Exchange

believes that requiring these disclosures will enhance transparency and enable investors to make

informed decisions about whether participating in the Overnight Trading Session or the PreMarket Session is appropriate for them, consistent with the investor protection objectives of the

Act. These proposed disclosures are also consistent with FINRA Rule 2265, which separately

See supra notes 5 and 6.

requires brokers to affirmatively disclose to investors that extended hours trading carries greater

risks than trading during Regular Trading Hours.

Market Surveillance

The Exchange believes that extending its existing surveillance programs and compliance

infrastructure to the Overnight Trading Session is consistent with the Act because it provides that

trading during overnight hours is subject to the same comprehensive regulatory oversight

applicable to trading during other sessions, including automated trade surveillance, routine

Member examinations, and an exam-based regulatory program. Exchange staff will be available

during the Overnight Trading Session to maintain a fair and orderly market, issue necessary

rulings, implement trading halts, and take any other action that may be necessary, consistent with

the Exchange’s obligations under the Act and its rules.

Competitive Considerations

The Exchange also believes the proposal is consistent with the Act because it will foster

competition by providing investors with access to another regulated national securities exchange

that offers trading during overnight hours, consistent with similar proposals approved by the

Commission for other national securities exchanges. The Exchange operates in a highly

competitive market in which investors seeking overnight access to U.S. equities currently resort

to alternative trading systems, foreign securities markets, and other venues. Enabling 23x5

Trading on the Exchange will allow it to compete for order flow from these investors, which the

Exchange believes will increase market accessibility, promote capital formation, and facilitate

portfolio management.

Self-Regulatory Organization’s Statement on Burden on Competition

The Exchange does not believe that the proposed rule change will impose any burden on

competition that is not necessary or appropriate in furtherance of the purposes of the Act. The

Exchange believes the proposed rule change will, in fact, enhance competition by providing

investors with access to an additional regulated national securities exchange offering trading

during overnight hours.

The Exchange does not believe the proposed rule change will impose any burden on

intramarket competition that is not necessary or appropriate in furtherance of the purposes of the

Act. The Overnight Trading Session will be available to all Members on an equal and nondiscriminatory basis. All Members will have the same opportunity to enter orders, access

liquidity, and participate in trading during the Overnight Trading Session under the same rules,

order type eligibility requirements, and session designation framework applicable to all other

Exchange trading sessions. The proposed customer disclosure requirements under Rule 3.21(h)

will similarly apply uniformly to all Members that accept orders for execution during the

Overnight Trading Session and Pre-Market Session, ensuring that all customers receive

consistent information about the risks associated with trading during those hours regardless of

which Member they use. The proposed rule change does not create any special rights,

preferences, or advantages for any particular class of Member or market participant.

The Exchange does not believe the proposed rule change will impose any burden on

intermarket competition that is not necessary or appropriate in furtherance of the purposes of the

Act. To the contrary, the Exchange believes the proposed rule change will promote intermarket

competition by enabling the Exchange to compete with other national securities exchanges and

trading venues that currently offer, or are in the process of offering, extended overnight trading

in U.S. equity securities. Investors currently seeking overnight access to U.S. equities may resort

to alternative trading systems, foreign securities markets, or other off-exchange venues. By

enabling 23x5 Trading on a regulated national securities exchange, the Exchange’s proposal

provides investors with a regulated, transparent, and competitive alternative to these venues,

which the Exchange believes will benefit the national market system.

As noted above, the Exchange’s proposal is substantively consistent with similar

overnight trading proposals that the Commission has previously approved for other national

securities exchanges, including EDGX, 24X, NYSE Arca, and Nasdaq. The Exchange does not

believe that its proposal confers any competitive advantage on MEMX relative to other

exchanges that have received approval for similar frameworks. Rather, the Exchange’s proposal

places it on equal competitive footing with those venues, which the Exchange believes is

necessary and appropriate in furtherance of the purposes of the Act.

Furthermore, the Exchange’s proposal to condition commencement of the Overnight

Trading Session on satisfaction of the Equity Data Plan readiness requirements provides that

23x5 Trading will not commence until the consolidated data infrastructure necessary to support a

fair, transparent, and competitive overnight trading market is in place. The Exchange believes

this condition serves the interests of the national market system as a whole and does not impose

any burden on competition that is not necessary or appropriate in furtherance of the purposes of

the Act.

Self-Regulatory Organization’s Statement on Comments on the Proposed Rule

Change Received from Members, Participants, or Others

The Exchange neither solicited nor received comments on the proposed rule change.

III.

Date of Effectiveness of the Proposed Rule Change and Timing for Commission Action

The proposed rule change is filed for immediate effectiveness pursuant to Section

19(b)(3)(A) of Act 32 and Rule 19b-4(f)(6) 33 thereunder. The Exchange designates that the

15 U.S.C. 78s(b)(3)(A).

17 CFR 240.19b-4(f)(6).

proposed rule change effects a change that (i) does not significantly affect the protection of

investors or the public interest; (ii) does not impose any significant burden on competition; and

(iii) by its terms, does not become operative for 30 days after the date of the filing, or such

shorter time as the Commission may designate if consistent with the protection of investors and

the public interest. In addition, the Exchange provided the Commission with written notice of its

intent to file the proposed rule change, along with a brief description and text of the proposed

rule change, at least five business days prior to the date of filing, or such shorter time as the

Commission may designate.

As discussed above, the proposal is based on EDGX’s filing, and other exchanges have

similarly received approval to offer 23x5 trading. 34 Accordingly, the Exchange believes that the

proposed rule change is non-controversial and eligible to become effective immediately because

it would enable the Exchange to adopt a similar framework for 23x5 trading as the previously

aforementioned exchanges. Moreover, the proposed change would promote the maintenance of a

fair and orderly market and the protection of investors and the public interest. The proposed

amendments are narrowly tailored to accommodate the framework of 23x5 trading that has been

approved by the Commission while preserving the integrity, efficiency, and investor protections

of the Exchange’s existing trading rules. The Exchange also believes that the proposed rule

change would not significantly affect the protection of investors or the public interest or impose

any significant burden on competition because the changes are based on the approved rules of

another national securities exchange that the Exchange proposes to adopt in substantially similar

form. The differences between the proposed rules and EDGX’s rules described above are based

on different functionality offerings but ultimately are not inconsistent with the shared purpose of

See supra notes 5 and 6.

enabling 23x5 trading, which promotes competition and is in the interest of investors and the

investing public. 35

For all the foregoing reasons, this rule filing qualifies for immediate effectiveness as a

“non-controversial” rule change under paragraph (f)(6) of Rule 19b-4. 36 At any time within 60

days of the filing of the proposed rule change, the Commission summarily may temporarily

suspend such rule change if it appears to the Commission that such action is: (i) necessary or

appropriate in the public interest; (ii) for the protection of investors; or (iii) otherwise in

furtherance of the purposes of the Act. If the Commission takes such action, the Commission

shall institute proceedings under Section 19(b)(2)(B) 37 of the Act to determine whether the

proposed rule should be approved or disapproved.

IV.

Solicitation of Comments

Interested persons are invited to submit written data, views and arguments concerning the

foregoing, including whether the proposed rule change is consistent with the Act. Comments

may be submitted by any of the following methods:

Electronic Comments:

•

Use the Commission’s internet comment form

(https://www.sec.gov/rules/sro.shtml); or

•

Send an email to rule-comments@sec.gov. Please include file number

SR-MEMX-2026-28 on the subject line.

As noted, these differences include order queuing functionality which the Exchange does not provide, as

well as differences in order types and modifiers as well as certain session restrictions related thereto.

17 CFR 240.19b-4(f)(6).

15 U.S.C. 78s(b)(2)(B).

Paper Comments:

•

Send paper comments in triplicate to Secretary, Securities and Exchange

Commission, 100 F Street NE, Washington, DC 20549-1090.

All submissions should refer to file number SR-MEMX-2026-28. This file number

should be included on the subject line if email is used. To help the Commission process and

review your comments more efficiently, please use only one method. The Commission will post

all comments on the Commission’s internet website (https://www.sec.gov/rules/sro.shtml).

Copies of the filing also will be available for inspection and copying at the principal office of the

Exchange. Do not include personal identifiable information in submissions; you should submit

only information that you wish to make available publicly. We may redact in part or withhold

entirely from publication submitted material that is obscene or subject to copyright protection.

All submissions should refer to file number SR-MEMX-2026-28 and should be submitted on or

before [INSERT DATE 21 DAYS AFTER DATE OF PUBLICATION IN THE FEDERAL

For the Commission, by the Division of Trading and Markets, pursuant to delegated

authority. 38

Sherry R. Haywood,

Assistant Secretary.

17 CFR 200.30-3(a)(12).

This is a copy of a public record, reproduced as it was published. It is not legal advice, and it may not be the version a court would rely on. Check the official source before you cite it.