For two weeks, traders had been writing off a Federal Reserve rate hike this month. Then the Bureau of Labor Statistics published the September consumer price index on Wednesday, and the odds of an Oct. 28 hike roughly doubled in a few hours.

Consumer prices rose 3.7% from a year earlier, up from 3.4% in August and above the 3.6% economists expected, the BLS said. Prices climbed 0.6% from August. The details were more worrying than the headline.

What the Report Showed

Core CPI, which strips out food and energy, rose 0.3% in the month and 2.6% over the year, against forecasts of 0.2% and 2.5%, CNBC reported. In August the annual core rate was 2.4%.

Gasoline did most of the lifting. Prices at the pump jumped 9.1% in September alone, accounting for about half of the monthly gain in headline inflation, and are up 34% from a year ago, according to the BLS figures cited by CNBC. Apparel, which is sensitive to tariffs, rose 0.3% on the month and is up 3.4% from a year earlier.

It Was Not Only Fuel

The story would be simpler if energy explained everything. CNBC's breakdown attributes the rise mainly to the Iran war, which has pushed up crude oil and the fuels refined from it, but economists also pointed to tariffs, the construction of artificial-intelligence data centers and strong consumer demand in categories such as travel.

Mark Zandi, chief economist at Moody's, called the overall report uncomfortably strong. Sonu Varghese of Carson Group said the report was hot beyond fuel prices, noting that core inflation had run at a 3.7% annualized pace in September.

How Markets Reacted

Stocks fell. The S&P 500 lost 1.11% to 7,718.94, its first drop of at least 1% in more than 50 trading days, Xinhua reported. The Dow slipped 0.09% to 51,621.48. The Philadelphia Semiconductor Index fell 4.3%, a sixth straight losing session, and AI-linked names including Oracle, CoreWeave, Nebius, Marvell and Advanced Micro Devices tumbled. Investing.com said the Nasdaq dropped nearly 2%.

Treasury yields whipsawed. The 10-year yield jumped above 5.32% right after the report, then eased to about 5.19% by the close as investors sought safety, according to Xinhua. Earlier this month it had touched a 24-year high of 5.365%, Quartz noted.

Some of the day's pressure was unrelated to inflation. Micron fell on worries about a Chinese memory-chip rival, and Bank of America slipped after profits disappointed, Yahoo Finance reported. But the sharpest selling hit the stocks that are most sensitive to interest rates and most dependent on future earnings.

The October Question

CME FedWatch put the chance of a hike at the Oct. 28 meeting at about 22% the day before the report. By Wednesday it had jumped, with readings during the day ranging from the mid-30s to 49% depending on the hour, and Xinhua put it at 37% at the close. Traders also priced about a 91% chance of at least one hike by December.

Chair Kevin Warsh has said September's increase removed "a dose of accommodation," according to Yahoo Finance. The Fed raised its target range to 3.75% to 4% on Sept. 17, as Blogerroom covered in its report on the unanimous 12-0 hike.

Politics complicates the decision. UBS has called a hike on the eve of the Nov. 3 midterm elections politically untenable and expected December, according to the same Yahoo report, which noted such a move would be rare. RSM economist Joseph Brusuelas saw little sign of disinflation, expected more than one further hike, and questioned October while pointing to December.

The labor market has given the doves an argument. Blogerroom reported that payrolls rose by only 29,000 in September. Wednesday's report suggests the inflation side of the Fed's mandate is the louder one right now.

A Global Pattern

The same energy shock is driving prices up elsewhere. Blogerroom covered euro-area inflation hitting 3.8% in September, and central banks from Canberra to Mumbai have been raising rates. A Fed that holds in October while inflation accelerates would stand apart.

My view: the October odds will keep swinging, and they should be read as a measure of how much the market doubts the Fed's willingness to move before an election. The more telling number is the 91% chance of a hike by December. Markets have stopped debating whether the Fed hikes again and are arguing only about the date.

What to Watch Next

Producer prices were due on Thursday, with forecasts of a 0.5% monthly rise, followed by retail sales. Then comes the Oct. 28 meeting, where the statement and Warsh's press conference will signal the path. The next CPI report arrives on Nov. 10, a week after the midterms.

This article is general information, not financial advice.