The Always-On Exchange: Rebuilding Market Infrastructure for 24/5 and Beyond

US equity markets are moving towards a much longer trading day. Major exchanges are preparing for 23-hour trading, five days a week, while the Securities and Exchange Commission (SEC) recently devoted a roundtable to the operational, resilience, clearing and market-structure implications. Overnight trading remains relatively small – accounting for less than 1% of NMS stock volume, according to SEC Commissioner Hester Peirce – but the infrastructure supporting it is expanding.

The shift extends beyond the US. The London Stock Exchange has announced LSE 24, a separate 24/5 venue scheduled to begin with exchange-traded products in the first half of 2027, subject to regulatory approval.

Yet ‘always-on’ can mean different things. Investors may have access to liquidity across multiple venues and sessions without any individual venue operating continuously.

“I’d highlight the difference between a market being available – being able to trade US equities 24 hours a day, five days a week by going to different venues – and a venue itself being available 24/5 or 24/7, where you can trade in one location,” says Matt Barrett, Co-Founder and CEO of Adaptive, specialists in custom trading technology solutions. “A retail trader may already be experiencing something akin to continuous US equities trading, but what’s actually happening underneath is quite a complicated choreography.”

While retail and overseas investors are driving demand for extended US equity trading, Sylvain Thieullent, CEO of Horizon Trading Solutions, the electronic trading technology provider, points to the institutional need to manage risk outside conventional market hours.

“From an institutional standpoint, and not specifically in equities, it’s about having the capacity to trade at any time, including over the weekend, for hedging purposes,” he says. “If there’s a crisis somewhere in the world at three o’clock in the morning – a war breaks out, for example – firms don’t want to wait until Monday morning at eight o’clock to start trading and hedge what they have on their books.”

The traditional market close has long provided exchanges and trading firms with a window in which to reset systems, update data, perform maintenance and prepare for the next session. As trading hours expand, that window is shrinking, forcing more of these activities to take place while markets remain open.

Engineering out the maintenance window

Tim Field, VP of Engineering at HPR, the high-performance trading infrastructure provider, argues that continuous operation requires a fundamental change in how trading systems are designed.

“The most relevant lesson is that you cannot retrofit ‘always-on’ – it must be an assumption at inception,” he says. “Historically, firms could build on a foundational assumption that the US trading day was 6.5 hours, leaving ample time overnight to shut down, archive, reset, and load fresh state. That window did real work. A significant amount of reference data changes day over day: which symbols are available for trading, corporate actions, new IPOs. New connections and new client accounts were provisioned overnight so the system could come up clean in the morning. Operational teams could start systems early in pre-market, run health checks, and triage issues well before the open. In a 24/5 or 24/7 market, that window disappears. Systems have to be dynamic; configuration changes need to be accepted during live trading.”

Failure recovery presents a particular challenge. A system may be able to withstand a component failure but still rely on the next market close to restore full redundancy. In continuous markets, that recovery must happen while trading continues.

“There is absolutely a significant difference in engineering approach between building a system that is resilient in the face of a failure but gets several hours in the day to recover itself, and one that has to operate continuously,” says Barrett. “We have a phrase for it internally: reducing the ‘time at risk’. If a node fails, the engineering effort goes into making the period before a new node can join the cluster and participate in transactions as short as possible.”

Maintaining the same availability standards across a much longer trading day places greater demands on infrastructure and recovery processes. Distributed architectures can help by shifting resilience towards individual services rather than relying on recovery of an entire platform.

“With microservice architecture as the driving force, you focus on the reliability and resiliency of individual pieces of business functionality,” says Jim Downs, Founder and CEO of Connamara, the exchange and trading technology provider. “If a service fails, the software automatically starts a new replica, rehydrates it with the data it needs and brings it back to its previous known state. And then it’s a question of optimisation. If a microservice took 15 seconds to rehydrate, that isn’t acceptable, whereas 15 milliseconds might be.”

Longer runtimes create additional challenges. Beth Geething, Product Manager Lead at HPR, points to ‘runtime decay’ in conventional software, including memory fragmentation, lock contention, queue saturation and garbage collection, which can gradually erode system performance and predictability. Patching, restarts and other routine maintenance must also be accommodated without disrupting trading.

When there is no longer a natural ‘day’

The concept of a trading day is embedded throughout exchange technology, from order handling and reference data to reconciliation and regulatory reporting.

“One of the things you need to do is lose the concept of the solar day,” says Downs. “However, you still need the concept of a trading day because statements have to be produced, reconciled and sent to customers and, more importantly, regulatory reporting has to happen on a trade date. You have to design your data model so that the trade date doesn’t necessarily correspond with the solar day.”

That distinction affects everything from the definition of a day order to the timing of regulatory reporting. Exchanges must also accommodate the daily changes to listed securities, a process that becomes considerably harder as the interval between trading sessions shrinks.

“Particularly in US markets, one of the most substantial differences people miss when comparing equities with FX and crypto is that our reference data changes every single day,” says Quito Zuba, COO of MEMX, the US equities exchange operator. “In FX markets, you might add a currency pair every couple of months. In crypto there can obviously be more than that, but you’re generally adding an individual pair and can control that environment. In equities, we’re constantly adding and removing symbols, changing listings, dealing with reverse splits, splits and all the corporate-actions data that we have to get right as an industry.”

For exchanges preparing to operate 23 hours a day, processes that previously had several hours must be completed within a much narrower window.

“You’re only as good as your worst process,” says Zuba. “When you’re rolling over in an hour you have to look at all of those things. We have to performance-tune literally everything, from our data-centre access rules and entitlements to user-administration tools – all the things that become easier when you have six or seven hours to roll over a system. All those crutches disappear.”

Navigating a fragmented trading day

Exchanges, ATSs and other liquidity providers are unlikely to extend their operating hours simultaneously. The transition could leave brokers and trading firms navigating overlapping sessions with different liquidity profiles. Thieullent expects this to complicate liquidity discovery and venue selection.

“The transition is what’s going to be particularly complex because people are going to launch initiatives,” he says. “Some will work, some will stay and some investment will be wasted. You don’t know who the winners will be, so firms will have to decide where to connect. With MiFID best execution, for example, you need to connect to the appropriate venues to provide best execution for your client. Am I connecting to the right liquidity pools?”

The issue is already apparent in US equities, where overnight activity remains concentrated in a relatively small number of stocks. As more venues extend their hours, brokers will need to assess which offer meaningful liquidity at different times, while managing the associated market-data and connectivity requirements.

Smart order routing and execution algorithms will also need to adapt to changing patterns of liquidity and price discovery. A venue may be technically available throughout an extended session without offering sufficient liquidity to execute an order efficiently.

The rest of the market has to stay open too

The experience of Blue Ocean, the overnight US equities trading venue operator, illustrates how post-trade infrastructure has progressively adapted to overnight execution.

“When we started trading in 2021, DTCC opened at 4am, so we batched up all our trades and sent them to DTCC at 4am,” says Blue Ocean CEO Brian Hyndman. “They subsequently moved that to 1:30am and, last June, they started at 8pm. So they’re essentially 24/5 now. We think that really de-risked the industry because DTCC is now open when we start our overnight session at 8pm.”

While DTCC has extended its clearing operations to support longer trading hours, FINRA has also expanded the operating hours of its Trade Reporting Facilities, with the US Securities Information Processors also preparing to extend their services to support 23/5 trading.

Weekend trading introduces a further complication. When RQD Clearing, the US clearing and custody services provider, began supporting Blue Ocean’s overnight session, trades could not be submitted to NSCC for clearing until 4am – eight hours after trading began.

As RQD CEO Michael Sanocki explains: “If trading expands to weekends without clearing infrastructure keeping pace, you could be extending that gap to as much as two days. That creates additional counterparty exposure before trades enter central clearing. From my perspective running a clearing firm, the biggest concern is how much exposure can build up between counterparties and the venue during that window and what safeguards are in place.”

Even if clearing infrastructure keeps pace with trading, participants still need access to cash and collateral outside conventional banking hours.

“The hurdle you have to jump on the clearing side, especially with pre-funding, is how you move funds on a weekend, holiday or outside business hours, particularly if even the Fed window is closed,” says Downs. “For me, it’s more about the funding side. That’s constrained at the highest level: how can a bank move funds between accounts?”

The pressure extends across the post-trade lifecycle. Adaptive’s Barrett argues that batch processes designed around T+1 or T+2 workflows will become increasingly difficult to sustain, while HPR’s Field highlights the need for configuration and reference-data changes to propagate across interconnected systems during live trading. Risk management, collateral, reconciliation and settlement processes will all need to adapt.

Many of these dependencies sit outside an individual exchange’s control. MEMX has been working with other market participants to address issues such as common reference data and coordinated operational processes, recognising that inconsistencies between systems can affect the wider market.

“This is about all of us being successful together,” says Zuba. “It would be far-fetched to say one exchange was successful and another wasn’t. The blast radius is the market. Everything is connected. The question is whether we as an industry can do this in concert with each other and still provide the stability that people have grown accustomed to.”

The economics of staying open

Extending trading hours carries costs that may be difficult to recover while overnight volumes remain relatively low. Exchanges must maintain their infrastructure and market operations for longer, while brokers face additional expenditure on connectivity, market data, risk management and support. Staffing is another challenge, as Blue Ocean discovered when it began operating overnight.

“Initially, we had staff here in the US. At some point, people get burnt out. They’re working a graveyard shift and it’s really difficult,” says Hyndman. “Ultimately, we’re firm believers that you have to have boots on the ground in the areas you’re serving. Having people in those jurisdictions is important not only for their mental wellbeing, but also for having relationships with local people on the ground.”

Global Tier 1 firms can draw on existing follow-the-sun operations, while smaller regional firms face a more difficult investment decision. Thieullent expects competitive pressure to push some brokers towards longer hours even where the immediate commercial case remains uncertain. As he puts it, the prevailing attitude may become: “We have to do it, but we don’t necessarily want to do it.”

Legacy technology adds to the cost. Platforms designed around fixed trading sessions may require substantial re-engineering, while the commercial returns will vary considerably. Some businesses, including those operating in prediction and event-driven markets, depend on weekend activity. Others may need continuous trading capability primarily to manage risk during exceptional events, leaving them supporting expensive infrastructure through periods of relatively limited activity.

The last hour – and then the weekend

The remaining breaks in the trading week provide time for operational processes that have yet to become fully continuous. But those periods can also contain significant trading demand.

“Eight to nine is what the ATS world calls the ‘golden hour’,” says Hyndman. “That’s where you get all this retail activity and all the pent-up demand over the weekend. At 8pm on Sunday, that’s our busiest hour of the week. The ATSs aren’t heartbroken that the exchanges are pausing for that hour, but I do think they’re going to reconsider it.”

Moving towards 23/5 compresses the daily operational window into an hour. Moving to 24/5 removes that window but retains the weekend. Genuine 24/7 trading would eliminate both.

Exchanges and technology providers have demonstrated that matching engines can operate continuously. The challenge now is to bring the surrounding market infrastructure onto the same timetable, so that trading, risk management and post-trade processes can function without relying on the market close.

Explore the Future of Exchange Infrastructure at ExchangeTech Summit London 2027

The challenges of extended trading hours, resilient matching engines and evolving market infrastructure will be among the topics explored at A-Team Group’s ExchangeTech Summit London in May 2027. Bringing together exchange operators, trading venues, technology providers and market infrastructure specialists, the event will examine the architecture, connectivity and operational requirements shaping the next generation of financial markets.