• The S&P 500 erased its 2025 loss.
• Saudi Arabia is investing $600 billion in a series of deals with the U.S.
• Microsoft is laying off 3% of its workforce.

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

1. And just like that

The S&P 500 is back in the green. After being at one point down more than 17% for the year, the index rose 0.72% Tuesday to erase its 2025 loss. Hopes for a trade war détente and a softer-than-expected inflation report helped push stocks higher during the trading session. The Nasdaq Composite closed up 1.61% for its fifth-straight day of gains, thanks in part to a 5.6% boost in shares of Nvidia. But a nearly 18% drop in shares of UnitedHealth Group weighed on the Dow Jones Industrial Average, which sank 269.67 points, or 0.64%. Follow live market updates.

2. $600 billion 'bromance'

At the start of President Donald Trump's trip to the Middle East, the White House on Tuesday announced that Saudi Arabia has committed to investing $600 billion in the U.S. Speaking at the U.S.-Saudi Investment Forum in Riyadh, Trump praised the Saudi kingdom and its leader, Crown Prince Mohammed bin Salman, with one summit attendee describing their relationship as a "bromance for the ages." Trump also announced that the U.S. will remove all sanctions on Syria, and he met with Syrian leader Ahmed al-Sharaa in Saudi Arabia the next day. Other news that came out of the forum included Nvidia's plans to sell more than 18,000 of its latest AI chips to Saudi company Humain, and Saudia Arabia's approval of Elon Musk's Starlink for aviation and maritime use in the kingdom.

3. More tech layoffs

Microsoft is laying off 3% of its total workforce — about 6,000 people — the company said Tuesday. The cuts across all levels, teams and geographies likely represent the tech giant's largest round of layoffs since 2023, when it eliminated 10,000 roles, and follow a small round of performance-based cuts in January. "We continue to implement organizational changes necessary to best position the company for success in a dynamic marketplace," a Microsoft spokesperson said in a statement to CNBC. One objective of the new round of cuts, which are not related to performance, is to reduce layers of management, the spokesperson said.

4. IPO plans

Fintech company Chime filed paperwork on Tuesday to go public on the Nasdaq, and it wants to make one thing clear: "Chime is a technology company, not a bank," the digital banking firm said in its prospectus. The company brought in $518.7 million in revenue in the March quarter with 8.6 million active members, about 23% more users than the same time last year. Chime, which plans to file under the ticker symbol "CHYM," is only the latest emerging tech company to test the market's appetite for new offerings. Digital physical therapy startup Hinge Health said Tuesday it plans to raise up to $437 million in its upcoming IPO, while stock brokerage platform eToro priced its IPO above its expected range at $52 a share. CoreWeave, which reports its first-quarter earnings results after the bell Wednesday, debuted on the Nasdaq at the end of March.

5. 'Good at bad stuff'

Experts are sounding the alarm about the safety of artificial intelligence — or the lack thereof. As companies like Meta, Google and OpenAI race to stay competitive, AI players have shifted from focusing on cutting-edge research to prioritizing the development of revenue generating, consumer-ready AI services. In the process, they're increasingly taking shortcuts when it comes to the safety testing of their models, experts say. "The models are getting better, but they're also more likely to be good at bad stuff," said James White, CTO at cybersecurity startup Calypso.

— CNBC's Brian Evans, Yun Li, Jesse Pound, Kevin Breuninger, Natasha Turak, Kif Leswing, Lora Kolodny, Jordan Novet, Samantha Subin, Ashley Capoot, Hayden Field, Jonathan Vanian and Jennifer Elias contributed to this report.