The S&P 500 ended the week down 2%, closing at 7,354.02, as renewed geopolitical tensions over Iran's alleged ceasefire violation triggered a selloff in AI-linked technology and communication services stocks. The decline was concentrated in sectors most tied to the artificial intelligence boom, with communication services falling 6.2% and technology dropping 5.4%, while defensive areas like health care rose 7.9%.
What happened with Iran?
Markets had grown more comfortable with the US-Iran backdrop after a memorandum of understanding pointed toward a longer-term peace deal, including the reopening of the Strait of Hormuz, a critical chokepoint for global oil shipments. That optimism evaporated when President Donald Trump said Iran launched at least four one-way attack drones at ships crossing the strait, calling it a ceasefire violation. The Strait of Hormuz is a narrow waterway between the Persian Gulf and the Gulf of Oman, through which about 20% of the world's oil passes. Any disruption there can quickly raise energy prices and unsettle global markets. For more on how such incidents affect shipping and stocks, see Swiss Stocks Dip as Strait of Hormuz Incident Revives Shipping Jitters.
Why AI stocks were hit hardest
The selloff wasn't broad: only four of the S&P 500's 11 sectors fell for the week. But because the index is weighted by market value, a move in a handful of mega-cap names can outweigh what's happening in the rest of the market. When investors get nervous about geopolitics, they typically demand a higher "risk premium" — the extra expected return required to own stocks instead of safer assets like bonds. That pressure often hits long-duration growth companies first, where much of the value depends on profits expected far in the future. AI-exposed tech and communication services stocks fit that profile perfectly.
Company-specific news amplified the sector's weakness. Alphabet slid more than 8% after Bloomberg reported it may lose two senior AI researchers to Anthropic, a rival AI startup. That kind of talent departure can raise questions about a company's ability to maintain its competitive edge in the fast-moving AI race. For context on how tech stocks have been reacting to broader pressures, see Tech Stocks Lead Premarket Slide as US Trade Deficit Widens Sharply.
Health care bucks the trend
While tech and communication services struggled, health care surged 7.9% for the week. That divergence is a classic sign of a "risk-off" rotation: investors moving money out of high-growth, speculative areas and into defensive sectors that tend to hold up better during uncertainty. Health care is often seen as a defensive play because demand for medical products and services is relatively stable regardless of the economic or geopolitical climate.
A major deal also boosted the sector. Bio-Techne jumped 23% after agreeing to be bought by Merck KGaA in an all-cash deal at $73 a share. Such acquisition premiums can lift the entire sector by signaling that larger players see value in health care companies, even when the broader market is nervous.
What it means for investors
The week's action is a reminder that headline index moves can mask big differences underneath. The S&P 500's 2% decline was driven almost entirely by AI-exposed tech and communication services stocks, while other areas like health care actually rose. For everyday investors, this highlights the importance of diversification: a portfolio concentrated in a single hot sector can be much more volatile than a broad-based one.
Geopolitical events like the Iran ceasefire dispute are notoriously hard to predict, but their market impact often follows a pattern. When tensions rise, investors tend to sell first and ask questions later, especially in stocks with high valuations and long-duration profit expectations. That's exactly what happened this week with AI stocks. For more on how geopolitical risks interact with market moves, see Tech Stocks Slip as Oil Drops and Yen Tests Intervention Zone.
Looking ahead, investors will be watching for any further developments in the Iran situation, as well as the upcoming jobs report, which could reignite talk about Federal Reserve interest rate policy. For more on that, see Jobs Report Could Reignite Fed Rate Hike Talk as Chip Stocks Falter.
