No market-wide trading halt was triggered, but the thresholds became the day's talking point. Decrypt reported that the S&P 500 would have had to reach 7,150.41 points, 7% below the previous close, to stop trading across US exchanges for 15 minutes. At its worst point the index was still 3.2 percentage points away from that line.
So this was a heavy session, not a halted one. The distinction matters, because the halt mechanism is automatic and the conversation around it on Thursday was anticipation rather than event.
Key numbers
- 3.8% the deepest S&P 500 decline on Thursday, one day after a 1.6% gain
- $2.9 trillion of market value lost, which MarketWatch called the largest one-day loss on record
- Nearly 11% the fall in the semiconductor index, with Nvidia down more than 6%
- 7,150.41 the S&P 500 level that would have set off the first 15-minute halt
Semiconductors took the heaviest hit
Around 11 a.m. New York time, the Nasdaq Composite was down close to 5% and the S&P 500 down 3.2%, according to Decrypt. MarketWatch described it as the worst day for technology stocks since 2020.
Decrypt tied the selling to Tuesday's midterm results and what a Democratic sweep might mean for the companies building AI infrastructure, data centers above all. Ipek Ozkardeskaya, senior analyst at Swissquote Bank, told Reuters she suspected the aggressive AI buildout would attract scrutiny.
The move reached other assets. Decrypt reported that bitcoin slipped under $76,000 and that roughly $428 million of leveraged long positions in crypto were liquidated inside an hour.
What a circuit breaker actually does
US equity markets carry three automatic thresholds, each measured against the prior session's S&P 500 close. A 7% fall, Thursday's 7,150.41, pauses trading for 15 minutes. A 13% fall, at 6,689.09, pauses it again. A 20% fall, at 6,150.89, closes the market for the rest of the day.
Timing is part of the rule. The 7% and 13% levels stop applying after 3:25 p.m. New York time, while the 20% level stays live until the close. A halt covers every US-listed stock, Nasdaq names included, not only the S&P 500 members.
In plain words: a circuit breaker is a pause button written into exchange rules rather than a decision anyone makes on the day. When prices fall far enough and fast enough, trading stops for a set number of minutes so orders can be rerouted and information can spread. It does not change the direction of the market; it changes the speed at which the market can move.
What the reports confirm, and what they leave open
Wednesday is the comparison that gives Thursday its shape. Decrypt reported that the S&P 500 had risen 1.6% that day, its strongest single session in three months, with the Dow Jones Industrial Average adding more than 1,500 points. President Donald Trump posted on Truth Social the same day about record highs and Americans' retirement accounts.
I went through both reports, and neither gives a closing level for Thursday. The 3.8% is the intraday low point, and the $2.9 trillion is MarketWatch's estimate of market value lost. Decrypt also lists inflation and the uncertain path of Federal Reserve policy as pressures on the session, without separating how much of the drop belonged to which.
What to watch
- Friday the US October employment report, which Decrypt notes investors were waiting on for guidance on monetary policy