• Market watchers are waiting for today's key Federal Reserve interest rate cut decision.
• Alaska Airlines and Hawaiian Airlines can merge after a DOT review.
• What's next for Big Tech?

Here are five key things investors need to know to start the trading day:

1. Ready for Fed

The S&P 500 ended Tuesday little changed as traders await the Federal Reserve's key interest rate cut decision (more on that below). The broad-market index touched a record high earlier in trading and ended the day off the mark at just 0.03% higher. The Dow Jones Industrial Average inched down 15.9 points, or 0.04%, after also hitting a fresh record during the session. The Nasdaq Composite added 0.2% for the day. The record highs for the S&P 500 and the Dow come during a historically tough period for the market, as September has been the worst month for the benchmark over the past 10 years, according to FactSet data. Follow live market updates.

2. Rate expectations

Federal Reserve meetings are often predictable events, with policymakers telegraphing their intentions ahead of time — but this time there's an air of mystery. Fed watchers are pretty sure there will be some kind of rate cut, but they're divided on if it will be the traditional quarter-percentage-point, or 25-basis-point, rate reduction, or a more aggressive 50-basis-point cut. The Federal Open Market Committee has held its benchmark fed funds rate at the highest level in 23 years, a range between 5.25%-5.5%, since it last raised rates in July 2023. Markets will also be watching to see what signals meeting participants send about where rates are expected to go from here, as well as unofficial forecasts for unemployment, gross domestic product and inflation.

3. Merger in the air

Alaska Airlines and Hawaiian Airlines are cleared for merging. The Department of Transportation said Tuesday that the two carriers could go through with their $1.9 billion merger agreement, but they must maintain the value of their frequent-flyer miles programs and maintain several key routes. They also must keep "essential air support" for rural areas, as well as current levels of service for passenger and cargo routes between the Hawaiian islands, U.S. Secretary of Transportation Pete Buttigieg said. The two airlines said in December, when they announced plans to combine, that they would keep each carrier's brand but operate under a single platform.

4. What's next for Big Tech?

Tech transaction volume has plummeted, falling to $544 billion last year after peaking at $1.5 trillion in 2021, according to Dealogic. So far in 2024, tech mergers and acquisitions have hit $465 billion. Now, with the upcoming presidential election, Big Tech is "at a crossroads" after that slump in dealmaking, Sergio Letelier, Hewlett Packard Enterprise's head of corporate development, told CNBC's Jordan Novet. "We don't know which side of the fork the policy is going to go," he said. That's in part because neither party has offered much clarity on the matter. The Biden administration has thwarted the biggest companies from pursuing deals, but the regulatory environment could be poised for a shake-up with the election.

5. Snappy

Snap unveiled the fifth generation of its Spectacles augmented reality glasses on Tuesday after years of trying to break into consumer hardware. The latest glasses, which can overlay digital graphics onto the physical world, are only available for developers, who must commit to paying $99 a month for a full year if they want to develop any AR apps. Snap also said it's partnering with ChatGPT maker OpenAI on artificial intelligence tools for the glasses. Snap's announcement came days before rival Meta is expected to reveal its latest hardware. Read more about both companies' struggles with consumer hardware here.

— CNBC's Hakyung Kim, Jeff Cox, Leslie Josephs, Jordan Novet and Jonathan Vanian contributed to this report.