Key Highlights

● Arm Holdings (ARM) closed at $283.33 on Monday, down $26.99, one of the steepest drops among major chip stocks.

● Reports that OpenAI paused Training of some frontier models raised doubts about AI developers' appetite for computing power.

● A $25 billion Margin Loan backed by Arm shares, taken by SoftBank, was cited as an added source of pressure.

● The 10-year Treasury Yield reached its highest level since 2007, which weighs especially on high-flying growth stocks.

Arm Holdings (NASDAQ:ARM) sank on Monday, September 28, closing at $283.33, down $26.99 from $310.32 on Friday, a decline of about 8.7%. It was one of the steepest drops among major chip stocks and a sharp turnaround for a stock that had been one of the market's hottest performers in September.

Arm designs the chip architecture used in most of the world's smartphones and a growing number of Data Center processors, so it sits right at the heart of the AI hardware trade. The Nasdaq Composite fell 248.34 points to 26,820.38.

From Rocket to Reversal

The context explains the size of the fall. When a stock runs as far and as fast as Arm did in September, even a modest shift in sentiment can trigger heavy profit-taking. Market reports pointed to oil-driven Inflation fears and profit-taking after the run-up as key drivers, and one additional Factor cited was a $25 billion margin loan tied to Arm's share price.

Arm fell harder than most of its peers: Qualcomm (NASDAQ:QCOM) lost about 7.2%, Intel (NASDAQ:INTC) about 5.7%, Marvell (NASDAQ:MRVL) about 3.8%, AMD (NASDAQ:AMD) about 3.6% and Micron (NASDAQ:MU) about 2.6%.

The OpenAI Pause Shock

The whole chip sector was under fire on Monday. Over the weekend, reports said OpenAI had paused training of some frontier models. The reports raised doubts about how fast AI developers will keep buying computing power, and they hit chip designers and memory makers alike. Nvidia (NASDAQ:NVDA) was the lone standout, rising after it announced a $150 billion buyback increase.

Yields and Oil Pile on

Government bonds sold off hard, sending the 10-year Treasury yield to its highest since 2007 and the 30-year to its highest since 2004, a squeeze that hits stocks priced on distant profits. High-flying Growth Stocks like Arm tend to be especially sensitive to rising yields, because more of their value rests on profits expected far in the future. Crude prices edged higher after President Trump turned down Iran's plan to reopen the Strait of Hormuz, with Brent near $105.28 a barrel and West Texas Intermediate near $92.60.

Major indexes closed in the red. The S&P 500 declined 59.72 points to 7,683.69, the Dow Jones Industrial Average slid 347.11 points to 51,481.51, and the Nasdaq Composite retreated 248.34 points to 26,820.38.

Micron's Earnings Will Test the Chip Trade

The next big test for the chip trade comes Wednesday, when Micron reports earnings after the close. Its results and outlook will offer a fresh read on AI-related Demand after the OpenAI news.

The economic calendar is heavy: JOLTS Job Openings and consumer confidence on Tuesday, PCE inflation on Wednesday, ISM Manufacturing on Thursday and the September jobs report on Friday. Arm has shown this year that it can swing sharply in both directions, and it remains highly sensitive to AI headlines.