On the evening of May 15, US stock index futures rose during trading, continuing the upward trend driven by signs of slight inflation easing, indicating the possibility of rate cuts. With investors increasing their expectations of a rate cut by the Federal Reserve in September, Wall Street saw significant gains, with the dollar and bond yields declining.

This uptrend continued into after-hours trading, with S&P 500 futures rising by 0.1% to 5,338.75 points; Nasdaq 100 futures rose by 0.2% to 18,724.50 points; and Dow Jones Industrial Average futures rose by 0.1% to 40,092.0 points.

Data shows that the April CPI inflation rate was slightly below expectations, while the core CPI (including volatile food and energy costs) annual growth rate decreased from 3.8% in March to 3.6%.

Despite the decrease in inflation in April, it remains well above the Federal Reserve's annual target of 2%. Furthermore, this comes after strong growth in the Producer Price Index was reported the previous day. However, investors are still anticipating a 25-basis-point rate cut by the Federal Reserve in September, with the probability, according to the CME FedWatch tool, standing at 53.8%, up from 49.0% last week.

Stocks dubbed as "stock market hotspots" stagnated after two days of gains, with shares of GameStop Corp (NYSE: GME) and AMC Entertainment Holdings Inc (NYSE: AMC) both falling approximately 20% on the trading day. In after-hours trading, they further declined by 9% and 6.4% respectively.

Shares of insurance company Chubb Ltd (NYSE: CB) rose by over 7% in after-hours trading, reaching a historic high, following the announcement of a $6.72 billion investment by Warren Buffett's Berkshire Hathaway Inc (NYSE: BRKa) in the company.

After Cisco Systems Inc (NASDAQ: CSCO) reported quarterly earnings that exceeded expectations, its stock price rose by nearly 5%.