For decades, US stock exchanges have pressed pause every night, shutting markets for several hours. Yet after this December, the exchange servers will stay lit far longer as American equities move toward an around-the-clock 23-hour trading model.

Nasdaq, NYSE Arca, 24X National Exchange, and Cboe EDGX have laid out plans to add an overnight session from 9pm to 4am New York time, on top of the existing regular, pre-market, and post-market sessions.

This expansion, set to take effect on December 6, aims to capture growing demand from overseas investors while competing with crypto asset and prediction markets, whose 24/7 nonstop trading has already upended traditional notions of Wall Street's operating hours.

Overnight trading has existed for years, mainly through alternative trading systems, but accounts for a tiny share of overall activity. Data presented at a US Securities and Exchange Commission roundtable last week showed overnight trading made up about 1% of total equity volume in the second quarter. Though far smaller than daytime trading by any measure, overnight activity is growing fast, with volume surging 358% year over year.

The upcoming 23/5 trading model has sparked debate over how extended hours will affect global market participants. Supporters argue it will remove time zone barriers, making it easier for overseas traders to access US markets. Skeptics contend that thinner liquidity and wider bid-ask spreads will amplify trading risk.

Wall Street Without Sleep: Overnight Stock Trading Is Coming

David Easthope, a senior equity market analyst at Crisil Coalition Greenwich, said institutional investors' main concern is "market quality during extended sessions," while operational and staffing issues are not necessarily their top priority.

A survey his firm conducted last year of buy-side equity traders showed market participants were not enthusiastic about round-the-clock stock trading. With fewer active participants outside regular hours, investors may face lower volume, thinner liquidity, and wider bid-ask spreads.

The survey indicated this could bring added operational risk and complexity, and even affect traders' own physical and mental well-being. Since the survey was conducted in the second half of 2025, attitudes in this group have improved somewhat. Easthope said people now "feel more that this change is inevitable," especially as regulators continue to push related reforms.

For years, the concept of overnight trading has been welcomed by retail investors and trading platforms. Brian Hyndman, CEO of Blue Ocean Technologies, said once the new arrangements take effect in December, "the participants who have always been involved will show up and be ready." His company is one of the alternative trading system operators currently providing overnight trading services.

"But I still think there's a part of the industry that hasn't yet engaged, really the buy-side institutions and investment banks," he added. "They have been hesitant about participating."

Key market infrastructure providers are also preparing for the shift. The main institution responsible for clearing US equity trades, the Depository Trust & Clearing Corporation, moved to a 24/5 model in June, operating from 8pm Sunday to 8pm Friday New York time. The Securities Information Processor, which collects and disseminates quote and trade data, has also received regulatory approval to extend its hours to support overnight trading.

Joseph Saluzzi, partner and co-head of equity trading at Themis Trading, said supporters of the shift may be betting that once the infrastructure is in place, institutional demand will follow. However, he is skeptical of the transition.

"Institutional investors have no interest in trading in a market that is low-liquidity, wide-spread, and likely highly volatile," he said, adding that combined exchange pre-market and post-market volume accounts for only about 10% of overall trading activity. "In fact, if you wanted to make that argument, you could equally say the market is already trading too long, not too short."

Currently, institutional investors remain on the sidelines. Jeff O'Connor, head of market structure at Liquidnet, said if the December 6 changes improve price discovery during overnight hours, trading costs will eventually fall, helping institutional asset managers capture excess returns at night.

Overseas investors are naturally particularly active during overnight sessions. SEC data shows that in the second quarter, overseas investors accounted for 37% of overnight volume, compared with just 7% for institutional accounts.

This activity is also highly concentrated. In August, an average of just 15 stocks accounted for half of total overnight volume, often including shares of companies registered in mainland China and Hong Kong trading below $1. By contrast, it takes 256 stocks to account for half of regular session volume.

Currently, Nasdaq and NYSE core trading runs five days a week from 9:30am to 4pm Eastern Time. Both exchanges also offer pre-market and post-market sessions allowing limited types of trading: pre-market starts as early as 4am, while post-market trading runs from 4pm to 8pm.

After extended hours begin in December, exchanges will still pause for one hour from 8pm to 9pm for system maintenance and trade processing.

What Does the 23/5 Trading Model Mean for the US Long-Term Bull Market and Market Volatility?

The US stock market will soon move from a "New York trading day" to a near-round-the-clock market covering global time zones.

Nasdaq, NYSE Arca, 24X, and Cboe EDGX are advancing 23/5 trading around December 6, 2026, adding a night session from 9pm to 4am New York time while retaining a maintenance window from 8pm to 9pm.

The commercial driver comes from overseas investor demand and competition from continuous trading in crypto assets and prediction markets: second-quarter night session volume surged 358% year over year but still accounted for only about 1% of total US equity volume, with overseas investors and institutional accounts contributing 37% and 7% of night session volume respectively, showing global demand is growing while institutional participation remains limited.

The latest official progress indicates the reform has entered the system preparation stage: Nasdaq announced six user acceptance testing arrangements on September 28 and plans to launch pre-production testing on November 1; DTCC's NSCC extended to 24/5 clearing services in June, and the unified SIP has also been approved to extend operating hours, with plans to align with the December launch.

The core of Wall Street analysts' debate over the 23/5 model is whether longer trading hours can bring sufficient liquidity depth and reliable price discovery. 23/5 means five trading days a week with 23 tradable hours per day, while core trading sessions are retained. Its essence is expanding the time window for cross-time-zone capital access and information pricing.

Exchanges, night session platforms, and retail investors, especially in Asia, value trading convenience, while institutional investors focus more on bid-ask spreads, order depth, and execution costs for large trades.

Night session trading currently has both clear cross-time-zone demand and issues of highly concentrated volume and limited institutional participation. From a market microstructure perspective, when the order book is thin, buy and sell orders of the same size more easily move prices, and market makers may widen bid-ask spreads to compensate for inventory and hedging risk. Therefore, there is still a liquidity gap to fill between "being able to place an order anytime" and "being able to execute at a reasonable cost anytime."

Based on market microstructure reasoning, if orders are dispersed over longer periods in the early stage of reform while market-making capital does not increase in tandem, the thinner order book at night could amplify the price impact and temporary deviations of individual trades. As institutional participation, unified quotations, and arbitrage mechanisms improve, some information shocks originally concentrated at the next day's open may also be gradually digested in advance, so opening gaps may decrease, but total daily volatility will not necessarily fall.

For the US long-term bull market, 23/5 is expected to reduce friction for overseas investors, expand the potential capital pool, and lower the liquidity premium after liquidity improves. Its role is mainly reflected in market efficiency and valuation support, while long-term gains are still determined by corporate free cash flow, the full realization of AI-driven productivity transformation, interest rate expectations, the US Treasury yield curve, and the equity risk premium. Extending the trading clock can widen the channel for capital to enter US stocks, but sustained earnings growth determines how long a bull market that channel can support.

Wall Street financial giant JPMorgan has begun following Goldman Sachs, Jefferies, Yardeni Research, and other giants in turning bullish on US tech stocks, which has also driven institutional and retail investors to increasingly focus on buying-the-dip strategies during this week's US stock market pullback.

JPMorgan believes the overall valuation adjustment of the Magnificent Seven, the mega-cap tech giants that carry heavy weight in US equities, may be largely complete, and earnings growth is expected to become the main force supporting share prices again. JPMorgan said the forward 12-month price-to-earnings ratio of the Magnificent Seven relative to the broader market has fallen to about one standard deviation below the historical median, at a decade low.

Wall Street financial giant Jefferies recently said that driven by the twin engines of the AI investment boom and AI-related corporate earnings beating expectations, the S&P 500 is expected to surge to 8,000 by the end of 2026 and further reach 9,000 in 2027. Jefferies' core logic is clear and powerful: in a cycle where AI-driven earnings growth exceeds the historical average by more than double, fighting the earnings trend is dangerous. Jefferies' base case forecast of 8,000 for the S&P 500 in 2026 is based on earnings per share reaching $373, up 35% year over year and far above the consensus of 29%, along with a price-to-earnings multiple of 21.5 times.