Stock Market Midday, Sept. 30: Markets Rise on Softer Inflation Data, Investors Await Micron Earnings

As of 11:37 AM ET, the Nasdaq Composite (NASDAQINDEX:^IXIC) is up 1.02% to 27,072, the S&P 500 (SNPINDEX:^GSPC) has climbed 0.58% to 7,715, and the Dow Jones Industrial Average (DJINDICES:^DJI) slipped 0.03% to 51,336 following softer-than-expected inflation data.

Gold is down 0.60% to $4,157.79, and the 10-Year Treasury yield is up 2 basis points to 5.28%. Communication and utilities are leading the session gainers, while financial services and consumer defensive stocks are underperforming.

Today's biggest moves

Robinhood Markets fell despite positive analyst reaction to the launch of its AI-driven strategy tools. Investors are watching sector bellwether Micron Technology, when it reports earnings after the bell for guidance about the sustainability of the artificial intelligence (AI) boom. Moderna tumbled over 7% after a Citi downgrade.

What this means for investors

Positive news on the inflation front boosted stocks this morning, as August's Personal Consumption Expenditures (PCE) price index showed a 3.4% gain year-on-year. The number was lower than expected, and traders reduced their expectations of an October rate hike.

Meanwhile, concentration risk is back in the spotlight. The danger here is that if a couple of the big AI hyperscalers slip, it could have an oversized impact on the rest of the market. Plus, although major U.S. indexes are near all-time highs and appear relatively calm, single-stock volatility is rising. Market breadth -- the ratio of winning vs. losing stocks -- is deteriorating. Diversification and risk management are key.

Citigroup is an advertising partner of Motley Fool Money. Emma Newbery has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Micron Technology and Moderna. The Motley Fool has a disclosure policy.