What 23-hour stock trading changes in your market data

The US consolidated tape has always gone dark in the evening. Trades and quotes from every exchange flow through two securities information processors, the SIPs, which have operated from early morning to 8 p.m. Eastern. On 26 June 2026 the SEC approved amendments to both plans to run them from 9 p.m. Sunday to 8 p.m. Friday, with a one-hour pause each weeknight. The plans have scheduled the switch for Sunday 6 December 2026.

For someone who reads charts or pulls bars from an API, the change matters less for the overnight prices than for what it does to things that looked fixed: when a trading day starts, which trades a daily bar contains, and what a flag on a trade tells you. Most of that is written down in the plan documents. What your own tools will do with it mostly is not yet.

How it works

Trades come from two kinds of venue, travel through two pipes, and reach you through a vendor.

Exchanges report to the SIP for the stock's tape: the CTA plan for NYSE-, NYSE American- and regional-listed stocks, the UTP plan for Nasdaq-listed stocks. Each exchange decides for itself whether to trade overnight, and each needs SEC approval of its own rules to do so. Nasdaq's approval is Release 34-105199 of 10 April 2026 and Cboe EDGX's is Release 34-105587 of 29 May 2026. Within each group the overnight session is narrower than the brand suggests. Cboe's FAQ says BZX, BYX and EDGA will not adopt one, so only EDGX trades overnight. NYSE's FAQ for NYSE Arca says the other NYSE Group equities exchanges keep their current hours. Nasdaq's FAQ says Nasdaq Texas and PSX keep theirs.

Off-exchange trades, from alternative trading systems and wholesalers, are reported to a FINRA trade reporting facility, which passes them to the same SIPs. FINRA's filing of 15 July 2026 describes the rule in force before the change. The facilities run from 4 a.m. to 8 p.m. A trade executed between 8 p.m. and midnight is reported by 4:15 a.m. on the next business day, marked "as/of". A trade between midnight and 4 a.m. is reported by 4:15 a.m. A trade on a weekend or holiday can be suppressed from public dissemination altogether. The filing extends the facilities to the SIPs' new hours and requires a report within 10 seconds of execution. FINRA ties its implementation date to the SIPs'.

Vendors take the SIP feeds, an exchange's own feed, or both, and build the bars, snapshots and charts you actually see. Nothing in the plan documents tells them how to build a daily bar.

The trading day starts the evening before

The CTA plan's FAQ, version 1.2 of 29 September 2026, puts it in one sentence: "The entire 9:00 PM – 8:00 PM window is one trading day." Trades and quotes reported between 9 p.m. and midnight "are counted under the next calendar date for all statistical calculations (e.g., volume and revenue calculations)." Nasdaq, NYSE Arca and Cboe EDGX each state the same split in their own FAQs. A trade at 11:30 p.m. on Monday is a Tuesday trade, and one at 12:30 a.m. on Tuesday is also a Tuesday trade. NYSE Arca's FAQ shows the consequence for settlement: an overnight trade at 10 p.m. on 23 November 2026 has a trade date and clearing date of 24 November and settles on the 25th.

Holidays move with it. There is no session on the evening before a US market holiday, and the next session opens at 9 p.m. on the holiday itself if the following day is a business day. The CTA FAQ's own example is Christmas 2026, which falls on a Friday. There is no session on Thursday night or during Friday's regular hours, none on Friday night either, and trading resumes at 9 p.m. on Sunday 27 December.

The SIPs' published day also moves. In the CTA schedule, start of day goes from 1:30 a.m. to 8:55 p.m. the evening before. Symbol reference data, halts carried over from the previous session and short-sale restrictions are all published at 8:55 p.m. Late-reported trades from the session that just ended, and cancellations or corrections of its trades, can be submitted from 9 p.m. in the next one. A daily file built at midnight can still change.

What the tape marks, and what it leaves alone

The flag is the part most likely to be misread. The CTA FAQ says trades outside regular hours "will continue to use the 'T' sale condition and are not Last Sale eligible. This applies to both the Extended Early Hours (9:00 PM – 9:30 AM) and any trades after the 4:00 PM close." NYSE Arca and Cboe EDGX say the same about their own overnight trades. The UTP FAQ says its existing designated condition continues. So one condition covers overnight, pre-market and after-hours. Nothing on the trade distinguishes 11 p.m. from 7 a.m. except the timestamp.

What T does is set out in the sale condition table of the CTS output specification, version 2.12b of 1 July 2026: a T trade updates volume, and updates neither the consolidated last, high or low nor the participant's open, last, high or low. The UTP specification's matrix gives T the same row. In practice:

• Consolidated volume for a trade date includes the overnight trades from 9 p.m. the evening before. The CTA and UTP FAQs both say so.
• The consolidated high and low do not. An overnight spike will not appear in a high or low built from the SIP's consolidated fields. It will appear in a bar a vendor builds by aggregating every trade itself.
• The official open and close do not change. Nasdaq's FAQ says the 9:30 a.m. to 4:00 p.m. session, "marked by the Opening and Closing Crosses, will continue to set the prices". NYSE Arca will keep publishing its official closing price after the 4 p.m. auction with sale condition M. Arca's overnight session opens at 9 p.m. with no auction at all. Its first auction of the trade date is still the 4 a.m. early open.

Overnight price limits are new and narrow. From 9 p.m. to 4 a.m. static bands apply, provided by the listing exchanges and based on a percentage of the 4 p.m. official close and a consolidated round-lot sale in the evening. NYSE's FAQ puts them at 20%. From 4 a.m. to 9:30 a.m. there are no bands, as before. The exchanges also restrict what can trade: Nasdaq accepts only limit orders from 9 p.m. to 4 a.m., with no market or peg orders and no orders for the crosses, and cancels anything still resting at 4 a.m.

If the date slips, and what runs before it

The 6 December date is conditional. The CTA FAQ makes it "dependent on Listing Exchange readiness and regulatory approvals". The SEC planned for a delay in its order for 24X National Exchange of 7 August 2026. If the plans cannot meet 6 December, 24X may run its overnight session from 24 January 2027 without the SIPs, publishing the trades on its own proprietary feed instead. The relief ends when the SIP amendments are implemented or on 2 July 2027, whichever comes first. In that case overnight prices would exist only on venue feeds, and a tool on the consolidated tape would see none of them.

From 8 November to 5 December 2026 the CTA side runs a pre-launch: the overnight schedule in production, with trades and quotes for test symbols only. The UTP FAQ says there will be no UTP pre-launch. Some nights in November will carry test-symbol messages on one tape and nothing on the other.

Corporate actions take effect at 9 p.m.

A split or a dividend used to take effect in the hours between the evening close and the morning open, when nothing traded. Under 23-hour trading something may be trading. On the CTA tape, listing exchanges send corporate actions and adjusted closing prices in a file due by 8 p.m., and the SIP publishes them in the start-of-day reference data at 8:55 p.m. Nasdaq's FAQ says, pending SEC approval, that certain corporate actions and dividends "will be effective when trading commences at 9 p.m." Others will be halted from before 9 p.m. on the evening before the effective date until 8 a.m. on that date, under halt code M1. The list includes forward and reverse splits, symbol and CUSIP changes, spin-offs, mergers and dividends of 25% or more of the official close.

Under Nasdaq's proposal, the first trade on an ex-dividend date can print at 9 p.m. the evening before, against an adjusted reference price. Nasdaq's FAQ also warns that between its overnight session and the session that starts at 4 a.m., "reference data, including stock locate code assignments, can change". Code that caches a locate code or a symbol mapping for a whole calendar day will be wrong for part of it.

What each kind of tool will and will not show

Data APIs. Whether a daily bar is keyed by trade date or by calendar date is now a real question. Bars keyed by trade date put a Sunday 9:30 p.m. trade in Monday's bar. Bars cut at midnight in New York put it in Sunday's, a day with no regular session. Bars cut at midnight UTC happen to put 9 p.m. to midnight Eastern into the next day, but in winter they move the last hour of the late session there too. Alpaca's market data FAQ says a trade's timestamp is truncated "to the day (in New York) for daily bars", a rule that would put a Sunday night trade in a Sunday bar unless it changes. Massive's announcement of 26 August 2026 says product details "will be shared in the coming months". Venue feeds for overnight trading already exist. Alpaca documents a Blue Ocean ATS feed and a cheaper derived "overnight" feed whose trades, its docs say, "are 15 minutes delayed and adjusted to fit the bid-ask spread". Both are one venue's activity, not the tape.

Charting platforms. TradingView's support page describes a 24h session for "BOATS-supported US stocks", which merges regular, extended and overnight activity on intraday charts only. That is the Blue Ocean ATS, one venue. After the SIPs extend their hours, an overnight candle can come from the consolidated tape or from a single venue feed, and the two will not agree. Cboe's FAQ lists Cboe One among the feeds that will carry EDGX's overnight trades. That matters because TradingView's free US real-time data is the Cboe One feed, according to its data-coverage page. Daily candles are a separate matter. Whether a platform's daily bar includes overnight trading is not stated on any page cited here. See why two charts show a different daily candle.

Desktop trading platforms. Platforms here do not make the data. They display the feed you connect. Sierra Chart sells the US equities consolidated tape as an add-on. A platform fed from the tape can receive overnight trades once the SIPs carry them, if its data service passes them through. Session templates are the thing to check. A chart session defined as 4:00 a.m. to 8:00 p.m. will either drop the trades from 9 p.m. or fold them into the wrong day.

Calendars and trackers. A calendar that models only the regular session still names the right trade date, but it cannot tell you when that date began. exchange_calendars treats everything outside regular trading as closed. pandas_market_calendars adds pre- and post-market times only when asked and only where a calendar defines them. Neither card records a 9 p.m. start. Portfolio trackers that mark positions to "last price" will start moving in the evening if their feed carries overnight trades. Those that mark to the official close will not move until 4 p.m.

What you can do about it

Decide which day an overnight trade belongs to, and write it down. If you store trades or bars, keep two fields: the timestamp in UTC and the trade date as the plans define it, with 8 p.m. Eastern as the boundary. Every daily aggregate you compute should group by the second. Computing the trade date from the timestamp later, without a calendar, will put holiday-evening trades in the wrong place.

Do not use the T flag to mean "pre-market". It means "outside 9:30 to 4:00", from 9 p.m. the night before to 8 p.m. If you split sessions, split them by time: overnight before 4 a.m., early from 4 a.m. to 9:30, regular, and late after 4 p.m.

Ask your data vendor four questions before 6 December. Are daily bars keyed by trade date or by calendar date, and in which time zone? Does daily volume include overnight trades? Are daily highs and lows built from every trade or from regular-session-eligible trades only? Does the overnight data come from the SIP or from a single venue such as an ATS? Take the answer from their documentation, with its date, not from a support chat.

Re-check session templates and scheduled jobs. A job that builds yesterday's bars at 1 a.m., a chart session that starts at 4 a.m. and a cache that refreshes symbol data once a calendar day were all built on the old schedule. Their failure mode is quiet: a missing hour or a doubled one. The how-tos on backfilling minute bars and getting an exchange calendar as data describe the pieces that need the new boundary.

Check the first weeks against a second source. The plans' own FAQs leave room for the date to move, and the fallback runs on a single venue's feed. Compare a few symbols' overnight volume and trade dates across two sources in the first week, before you trust a backtest or a report that spans the change.