Three years later, Teevan became Nadella's third technical adviser -- and the first to have a background in AI. Then she became chief scientist, and her task was to imbue the company's products with the AI of the time. In 2019, Nadella made the bold decision to spend $1 billion to partner with OpenAI, the small but trailblazing company that was leading the field. Microsoft was given unbridled access to its technology. It was a risky bet -- even experts like Teevan, who'd seen OpenAI's progress over the years, were skeptical that the tech would make much of a difference.

Then, late in the summer of 2022, she was invited to a demo of OpenAI's latest large language model, GPT-4, at Microsoft's Redmond headquarters. It took place in a windowless, gray-carpeted conference room in Building 34, where Nadella works. Two OpenAI cofounders, Greg Brockman and Sam Altman, came bearing a laptop. Brockman started with the sort of demos Teevan had seen in an earlier model, GPT-3.5. The new model responded with more sophistication, but Teevan wasn't blown away. She knew how to break LLMs with requests that would expose the system as a sophisticated word jumbler. So she put it through its paces. At one point she asked it to write a sentence about Microsoft such that every word began with the letter G. The software whipped up a response, but it used the word Microsoft. Teevan challenged the answer, and GPT-4 admitted it failed -- but it also asked her, didn't you want the sentence to be about Microsoft? Then it offered her an alternate sentence that didn't use the company name.

Teevan was stunned -- not just by the way GPT-4 handled the problem, but by its self-awareness. She hadn't expected that kind of a performance for years, if not decades.

She left the meeting and started driving the 2 miles home. She was having a hard time focusing. She pulled off the road and turned into the parking lot of a 7/11. "I sat in my car and let out a full-on scream," she says. "And then I went home and drank." After the first whiskey, she put on a movie: Terminator 2.

Not long after, she came to work dressed as Sarah Connor, the film's feisty heroine. Teevan knew what she had to do. OpenAI may have created GPT-4, but her employer had the rights to exclusively build it into its products -- and could beat its fellow tech titans at the most pivotal moment since the arrival of the internet itself. A year and a half later, for the first time in its nearly 50 years, Microsoft became worth $3 trillion.

Two years after the demo that blew Jaime Teevan's mind, I'm seated among 5,000 or so people at a Microsoft sales team event. Held at the start of a new fiscal year, in July, it's an entire day of product demos and morale-building chats and speeches. The highlight will be Satya Nadella's keynote. Tens of thousands of Microsoft employees are streaming the event from desks, conference rooms, and, for those in distant time zones, kitchens and home offices to hear from their boss.

Onstage, an engineer who does client support work for the company's Azure cloud service -- a Softie with a Dave Grohl vibe -- explains how OpenAI-powered tools can transmogrify a workflow. He tells the crowd how a developer from the AI team had shadowed him while he worked with customers, then developed a bot to do much of his work -- better than he could, apparently. The bot launched in late 2023. "We've saved $100 million!" he says of the AI-based support program. "Thirty-one percent increase in first-call resolution! Twenty percent reduction in misroutes! Next year we'll save $400 million."