Microsoft (MSFT) has become the second publicly traded company ever to cross the $4 trillion market capitalization mark. Chip giant Nvidia (NVDA) previously passed the threshold on July 9.

Microsoft hit the milestone Thursday morning following its strong Q4 earnings report in which it also said its Azure business brought in $75 billion over the prior year. The company’s stock price has climbed more than 110% since the debut of OpenAI’s (OPAI.PVT) ChatGPT in Nov. 2022.

Microsoft uses OpenAI’s technologies across its enterprise and consumer offerings, including its Azure cloud services, while OpenAI uses Microsoft’s cloud infrastructure to power its AI capabilities.

The relationship has been a boon for both companies, with Microsoft seeing Intelligent Cloud segment revenue, which includes Azure, of $29.8 billion in Q4.

OpenAI has also benefitted handsomely, with the company saying it is now seeing $10 billion in recurring revenue, according to CNBC.

More recently, the relationship between the two companies, however, has taken a rocky turn, as the duo hash out the terms of OpenAI’s transition to its for-profit arm into a public benefit corporation overseen by its non-profit parent.

Microsoft isn’t leaning entirely on OpenAI when it comes to its AI expansion. The company has also developed its own Phi AI family of models, though they’re not as powerful as OpenAI’s most advanced models. Microsoft is also working on its own high-powered AI model called MAI-01 that would compete with OpenAI and Google’s best, according to The Information.

Microsoft, like rivals Amazon (AMZN) and Google (GOOG, GOOGL), is also spending billions on its AI buildout. In 2025, the company expects to pile some $80 billion into the effort, but so far, demand continues to outpace supply.

Microsoft has also managed to largely avoid tariff threats under President Trump, unlike Apple (AAPL), which has faced mounting pressure from the administration to move manufacturing of its devices from overseas to the US.

On the consumer side, Microsoft is preparing to end support for its Windows 10 operating system in October, which should give a boost to Windows 11 sales through the end of the year. The company also continues to roll out AI features for its Copilot AI assistant across its Microsoft 365 productivity suite, Edge browser, and Windows itself.

But Microsoft is also facing an FTC antitrust investigation over its relationship with OpenAI, according to The New York Times. And while an investigation doesn’t guarantee the government will file a lawsuit against the company, it’s a headwind worth tracking.