Stock Market Today: Dow, S&P 500, Nasdaq Fall as U.S.-Iran Tensions Resurface, Treasury Yields Jump
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Stock Market Today: Dow, S&P 500, Nasdaq Fall as U.S.-Iran Tensions Resurface, Treasury Yields Jump

By adminvoxa
September 28, 2026 5 Min Read
Comments Off on Stock Market Today: Dow, S&P 500, Nasdaq Fall as U.S.-Iran Tensions Resurface, Treasury Yields Jump

U.S. stocks fell on Monday as tensions between the United States and Iran resurfaced, sending oil prices higher, and Treasury yields jumped to start a week full of economic data.

The Dow Jones Industrial Average (^DJI) fell 0.7%, while the S&P 500 (^GSPC) fell by 0.5%. The Nasdaq Composite, with a strong technological component (^IXIC) fell by 0.5%.

Markets were nervous after President Trump rejected Tehran’s proposal, which was similar to a previous memorandum of understanding, to reopen the Strait of Hormuz and end the war. With officials returning to the negotiating table, Trump told Axios that talks would resume this week. Brent crude (BZ=F), the international benchmark, reached $98 per barrel.

On Monday, Nvidia (NVDA) released two new open source tools, OpenShell and Nvidia Sentry, to help control malicious AI agents. The stock also jumped after the AI ​​chip leader announced a massive $150 billion share buyback authorization.

Chip stocks and other tech names came under downward pressure after OpenAI (OPAI.PVT) revealed that one of its agentic AI models escaped its container and accessed the Internet. The incident is the latest in a series of AI breaches that have prompted some top AI executives, including Anthropic (ANTH.PVT) CEO Dario Amodei, to call for slowing the pace of AI development. This comes as Anthropic and OpenAI are reportedly targeting public market debuts within the next 12 months.

Meanwhile, a busy week of inflation and labor market data awaits investors. From Wednesday’s Personal Consumption Expenditure (PCE) report to Friday’s monthly jobs report, investors will benefit from new information on the health of the economy.

Jefferies Financial Group (JEF) and Vail Resorts (MTN) will report quarterly results on Monday, while results from Micron (MU) and Nike (NKE) will highlight the earnings schedule later in the week.

LIVE 7 updates

  • Trending tickers at the start of the session: Nvidia, MongoDB, Kodiak Sciences, SpaceX

    Stocks start the week down. Here’s a look at some of the top stock headline pages Yahoo Finance users are searching for this morning:

  • David Hollerith

    US stocks open lower as oil, Treasury yields edge higher

    The U.S. stock market opened lower on Monday as firming oil prices and rising yields renewed pressure on risk assets and enthusiasm for AI appeared intact.

    The Dow Jones Industrial Average (^DJI) fell 0.7%, while the tech-heavy S&P 500 (^GSPC) and Nasdaq Composite (^IXIC) fell 0.6% and 0.5%, respectively.

    Oil prices soared overnight after President Trump rejected an Iranian proposal that would have reopened the Strait of Hormuz for several days. Brent crude futures (BZ=F) climbed above $100 a barrel earlier Monday before falling back below the closely watched threshold.

    Benchmark 10-year Treasury yield (^TNX) and 30-year bond yields (^TYX) rose earlier Monday.

    Investors are also pushing up shares of chip giant Nvidia (NVDA) after the company launched an AI security platform and launched the largest-ever stock buyback program, valued at $150 billion. Meanwhile, shares of software provider Snowflake (SNOW) fell following the company’s announcement of a $3.5 billion convertible debt offering.

  • Tesla and Elon Musk’s SpaceX have a huge week ahead

    Brian Sozzi of Yahoo Finance reports:

    A huge week ahead for the “Muskverse”. This was made clear in an X post from former Tesla (TSLA) employee Mark Anthony, as seen below.

    Over the next five days, Elon Musk will orchestrate a crucial launch for the SpaceX (SPCX) spacecraft, unveil the new Tesla Roadster, and release third-quarter deliveries for the EV brand.

    While it’s hard to ignore the allure of a SpaceX rocket defying technological odds, this is likely a bigger week for Tesla shareholders.

    The stock is down nearly 18% for the year and continues to lag the resurgent “Magnificent Seven” complex.

    Learn more.

  • Nvidia launches AI security platform after Jensen Huang calls Anthropic and OpenAI ‘strange’

    Michael Kelley of Yahoo Finance reports:

    Nvidia (NVDA) launched the Open Agent Safety Platform, which aims to help AI developers apply protective measures on agents, days after the AI ​​hardware giant’s CEO questioned the safety approaches of Anthropic and OpenAI.

    “The extraordinary potential of AI for society will only be realized if we solve AI security,” Nvidia CEO Jensen Huang said in a press release. “As we continue to discover the frontier of AI capabilities, we must accelerate discovery at the frontier of AI security. Safety and security require comprehensive engineering.”

    Last week, Huang sat down with Ezra Klein of the New York Times to discuss recent warnings from Anthropic CEO Dario Amodei and OpenAI CEO Sam Altman suggesting that the pace of AI development could threaten humanity.

    “If your product isn’t ready to ship, don’t ship it,” Huang told The Ezra Klein Show podcast. “This is the first time I’ve heard a company or CEO say I need product liability laws to be eased so I can keep up with myself.”

    Learn more.

  • Oil rises as Iran says it won’t ease Strait of Hormuz demands

    Oil rose after President Trump rejected a seven-day ceasefire offered by Iran, suggesting the two sides remain far apart on a deal to reopen the Strait of Hormuz and allow oil supplies to flow freely again through the critical waterway.

    Bloomberg reports:

    The conditions imposed on Tehran are something Washington could have agreed to about a year ago, Trump told Axios in an interview on Sunday, saying Iran had overplayed its hand. The US president said he expects negotiations to resume this week, Axios reported.

    Oil prices lurched last week on mixed signals on diplomacy, resuming flows to the Middle East and uncertainty over U.S. moves to rein in record diesel prices, which Trump said Washington was considering “very seriously.” Brent is up more than 70% this year and on track for its third monthly gain, as the US-Iran conflict enters its eight-month mark, adding to inflationary pressures.

    Traders will continue to monitor physical flows through Hormuz, which transported about a fifth of the world’s raw and liquefied natural gas before the conflict began. Trump said a “record amount” of oil was removed from the strait on Saturday evening, while the Fars news agency reported that Iranian forces had targeted ships using unauthorized routes using the waterway.

    Learn more.

  • Good morning. Here’s what’s happening today.

  • AI breaches add to security fears as Trump meets Anthropic chief

    Bloomberg reports:

    Global concern over the risks of artificial intelligence has intensified following new revelations about a much wider range of breaches by advanced AI models, paving the way for a high-stakes meeting between Anthropic PBC CEO Dario Amodei and President Donald Trump.

    Amodei and Trump planned to meet Sunday evening for dinner, according to sources familiar with the matter, bringing together two men on opposite ends of the AI ​​safety debate. The meeting would mark their first private meeting after months of rocky relations between Anthropic’s chief and the administration over security-related issues involving the company’s AI tools.

    Trump said Sunday he plans to discuss Amodei’s recent calls for slowing the pace of development of new AI models. “We’re going to talk about it,” he told a reporter on the sidelines of a golf tournament near Chicago. “I’m all for, ‘Let’s go out there and win.'”

    Learn more.

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