Rule 611 Repeal: Best Execution, SOR and TCA

By Medan Gabbay, Co-CEO, Quod Financial. October 2026.

Key Takeaways

On June 11, 2026 the SEC proposed rescinding Rule 611 of Regulation NMS (the Order Protection Rule) and Rule 610(e) (the locked and crossed markets prohibition). The proposal is not final. Industry analysts expect a final rule as early as Q1 2027.
Without Rule 611, the protected quote is no longer a mechanical floor. The duty of best execution under FINRA Rule 5310 becomes the primary standard for how NMS stock orders are routed and executed.
Best execution moves from “did we trade at or inside the NBBO” to “what did this order cost the end client, given what it was trying to achieve.” That is the intent-based model European markets have used under MiFID.
Routers built around trade-through compliance will need to route on intent: fill probability, venue quality, fees, information leakage and the objective of the order.
TCA becomes the evidence. Firms will need to justify routing decisions order by order, including the liquidity they chose not to take.

What Is Rule 611?

Rule 611 of Regulation NMS, known as the Order Protection Rule or the trade-through rule, was adopted in 2005 and implemented in 2007. It requires trading centers to maintain policies and procedures that prevent trade-throughs: executions at a price worse than the best displayed, automated quotation on another protected market. In practice it made the national best bid and offer (NBBO) a hard floor for every routing decision in US equities.

Rule 610(e) is its companion rule. It prohibits displaying quotations that lock or cross a protected quotation on another market.

What Is the Current Status of the Rule 611 Repeal?

June 11, 2026: the SEC proposed rescinding Rule 611 and Rule 610(e) in their entirety, along with related definitions in Rule 600.
June 17, 2026: the proposal was published in the Federal Register. Comments closed on August 17, 2026.
July 24, 2026: FINRA published Regulatory Notice 26-15, requesting comment on modernizing its best execution guidance under Rule 5310, partly in response to the SEC proposal.
Next: analysts expect a final rule in Q1 2027. Until the SEC adopts final amendments, Rule 611 remains in force.

The SEC’s stated reasons: Rule 611 increased cost and complexity, contributed to exchange proliferation and specialized order types, and created practical pressure to connect to every protected market. The Commission argues that modern routing and market data make the mandate unnecessary. It also acknowledged that Rule 611 may have benefited retail investors while hurting institutional investors.

How Does Removing Rule 611 Impact Me?

The impact depends on where you sit in the order flow.

Broker-dealers and agency desks: there would be no regulatory obligation to access every protected market. Which venues you connect to, and which quotations your router considers, becomes a policy decision you must document and defend under Rule 5310.
Institutional investors and asset managers: routers would no longer be forced to sweep small displayed quotes ahead of larger block, conditional or size-seeking opportunities. You also lose an automatic price guarantee, so you will need TCA that shows what your brokers did with your orders.
Retail brokers and wholesalers: the SEC does not expect significant changes in retail execution quality, given current wholesaler price improvement practices. The NBBO is likely to remain the reference point for retail.
Exchanges and ATSs: protected status would no longer guarantee order flow. Venues would compete on fill quality, fees, markouts and size.
Trading technology teams: logic written for Reg NMS (intermarket sweep orders, post-only repricing to avoid locking, connect-to-all routing tables) would need to be reviewed and re-engineered.

How Does Rule 611 Removal Impact Best Execution?

For twenty years, best execution in US equities has been anchored to price. Rule 611 and Rule 5310 pointed in the same direction: if you did not trade through the NBBO, you had met the most visible test. SIFMA’s comment to FINRA describes the rescission as ending that alignment, leaving best execution as the guiding principle for order handling and routing.

FINRA’s Notice 26-15 asks the questions this shift raises:

Will the NBBO remain an important benchmark once Rule 611 is gone?
How do transaction costs, including venue access fees, relate to the duty of best execution?
How should Rule 5310 apply to institutional orders, parent-child orders and algorithmic strategies?
What follows if firms connect to fewer execution venues?

The answer will look like the European model. MiFID never had a trade-through rule. European firms must take all sufficient steps to obtain the best possible result, weighing price, costs, speed, likelihood of execution and settlement, size and the nature of the order. For retail clients the measure is total consideration: price plus all costs. Best execution is defined by the intent of the order and the total cost to the end client, not by a single displayed quote.

What Can US Firms Learn From European Smart Order Routing?

Since 2008, Quod Financial has provided smart order routing across Europe’s fragmented markets to major Tier 1 and Tier 2 investment banks, private banks and regional brokerage powerhouses. That means routing across primary exchanges, MTFs, periodic auctions, dark pools and systematic internalisers, with no trade-through rule. Four lessons carry over directly:

Intent decides the route. A liquidity-seeking order and a passive accumulation order in the same stock should route differently, and the router needs to know which one it is handling.
The displayed best price is one input. Fill probability, venue toxicity, fees and post-trade reversion often decide the total cost more than the top-of-book price does.
Every decision needs a reason on record. Under a principles-based regime, “the rule required it” is no longer an explanation. The router has to record why it took or skipped liquidity.
Time must be precise. MiFID II RTS 25 requires clock synchronization to UTC within 100 microseconds for high-frequency activity. Without it, slippage and reversion measurements are unreliable.

What Systems Can Support Best Execution After Rule 611?

A trading stack ready for a post-611 market needs the following capabilities. Use this as a checklist for your OMS, EMS and smart order router.

Intent-based routing strategies: routing driven by the order’s objective (price improvement, size, speed, minimal footprint), not by a fixed sweep of protected quotes.
Configurable venue universe: venues selected per strategy and per instrument, with the rationale recorded.
Venue analytics in the routing loop: fill rates, markouts and reversion feeding back into routing decisions.
Fee-aware routing: access fees and rebates included in the cost of each routing option.
Locked and crossed market handling: if Rule 610(e) goes, routers must make sensible decisions when quotes lock or cross.
Decision-level audit trail: a record of why the algorithm placed, held back or declined liquidity at each step.
Microsecond timestamping and clock synchronization across order events, fills and market data.
Integrated TCA: pre-trade, real-time and post-trade analysis built on the same data the router uses.

These rules are new to the US. The technology is not. Multi-asset platforms built for European fragmentation already work this way.

What Should TCA Measure When Best Execution Means Total Cost?

In a recent engagement, a European bank asked Quod to build a TCA application around a simple principle: the firm defines its own cost methodology, and every number must be explainable. Its objectives are a useful guide to what US firms will need to measure once the NBBO is no longer the default answer.

Marketability-adjusted arrival shortfall. Measure slippage only while an order is marketable, and separate costs caused by the algorithm from costs caused by the client’s limit price. After Rule 611, this shows whether the routing decision cost money, not the constraint.
Opportunity cost and missed liquidity. Quantify unfilled marketable quantity and the visible liquidity the algorithm passed over, using the algorithm’s own audit stream to show why (venue restrictions, minimum fill size, risk limits, execution policy). This is the question a regulator will ask when a better price exists elsewhere and was not taken.
Reversion curves and alpha profiling. Track price movement before arrival and after execution, at intervals such as T-15 to T+15, to separate the firm’s own market impact from underlying momentum. This is how a firm proves that a route reduced information leakage.
Peer clustering. Compare execution quality against similar instruments grouped by market capitalization, ADV, volatility, spread and depth. When the NBBO stops being the only reference, fair comparison groups matter more.
Off-exchange and bilateral liquidity. Evaluate IOIs and bilateral fills against the prevailing public BBO at the moment of arrival and execution. Expect more flow in blocks, conditionals and bilateral channels once routers are no longer required to sweep displayed quotes first.
Market share and venue footprint. Measure on-exchange versus off-exchange share by instrument and segment. As firms connect to fewer venues, concentration becomes a best execution question in its own right.
No black box. Formulas and benchmarks defined by the firm, not imposed by a vendor. Any result can be interrogated step by step, including through an AI assistant asked to explain how a specific order’s arrival shortfall and opportunity cost were calculated. Under a principles-based standard, the firm must own and defend its methodology.
Data stays with the firm. Order, execution and client data processed within the firm’s own infrastructure.

How Should Firms Prepare for the Repeal of Rule 611?

Inventory every dependency on Rule 611 and the NBBO in routing logic, best execution policies, surveillance and client reporting.
Rewrite your best execution policy around order intent and total cost to the client.
Make venue connectivity decisions on evidence, and record the rationale.
Start capturing decision-level audit data now, so you have a baseline before the rule changes.
Synchronize clocks to microsecond precision across order, execution and market data.
Extend TCA beyond NBBO compliance to cover opportunity cost, reversion and venue quality.
Follow FINRA’s Rule 5310 guidance process, which will set the practical standard examiners apply.

Frequently Asked Questions About Rule 611

Has Rule 611 been repealed?

No. The SEC proposed its rescission on June 11, 2026, and the comment period closed on August 17, 2026. Rule 611 remains in force until final amendments are adopted, which analysts expect as early as Q1 2027.

Will best execution obligations still apply without Rule 611?

Yes. Broker-dealers remain subject to best execution under FINRA Rule 5310 and the federal securities laws. Without Rule 611, those obligations become the primary investor protection for order routing.

Will the NBBO disappear?

No. Consolidated quotations will still exist. The NBBO would become a benchmark rather than a mandatory floor. FINRA has asked the industry whether it should remain an important benchmark.

Will I still need to connect to every exchange?

Not by regulation. You will need to show that your venue selection supports best execution for your clients’ orders.

What is a trade-through?

An execution at a price inferior to a better displayed, protected quotation available on another trading venue at the same time.

How does US best execution differ from European best execution?

The US has relied on a price-based rule (Rule 611) alongside a principles-based duty (Rule 5310). Europe relies only on the principles-based duty, weighing price, costs, speed, likelihood of execution, size and nature of the order. Rescinding Rule 611 would bring the US much closer to the European approach.

What is the difference between a smart order router built for Reg NMS and one built for Europe?

A Reg NMS router is designed first to avoid trade-throughs and locked markets. A European router is designed to achieve the best total outcome for the order’s objective across a fragmented market, and to record why each decision was made.

About Quod Financial

Quod Financial builds multi-asset trading technology: order management (OMS), execution management (EMS), smart order routing (SOR), algorithmic trading, market making, transaction cost analysis (TCA) and connectivity across equities, FX, derivatives and digital assets. Quod has offered smart order routing in European markets since 2008, working with major Tier 1 and Tier 2 investment banks, private banks and regional brokerage powerhouses. Quod is ISO 27001 certified and SOC 2 Type II compliant.

Rule 611 Repeal: What It Means for Best Execution, Smart Order Routing and TCA