Billionaire Steve Mandel and his hedge fund Lone Pine Capital have been a great one to follow for individual investors. Although some hedge funds have a poor record of underperforming the broader market, Mandel has substantially outperformed the market over the past three years. So, when he makes a move in his portfolio, investors should pay attention.

One thing Mandel did during Q2 was sell off some of his Microsoft shares. Although it wasn't a massive move, the hedge fund reduced its position by about 5%. Then, Mandel used some of those funds to invest in another promising AI stock that has increased in value by nearly 800% over the past decade.

That stock? Amazon (NASDAQ: AMZN).

Amazon may not be the first company that comes to mind when you think about AI. Instead, it probably seems more like an e-commerce investment. While that sentiment is true for the consumer-facing portion, the reality is that a large chunk of Amazon's profits comes from AI-related revenue streams.

The biggest is from Amazon Web Services (AWS), its cloud computing arm. Cloud computing firms are having a strong year, thanks to the massive demand generated by AI workloads. Because more companies can't justify spending millions (or even billions) of dollars on a data center dedicated to training AI models, it's far more reasonable to rent computing power from a firm that already has the capacity. That's the idea behind cloud computing, and it has translated into strong growth for the business unit.

In Q2, AWS's sales rose 17% to $30.9 billion. That's strong growth, but it is a bit slower than its peers, Microsoft Azure and Google Cloud, which each grew revenue by more than 30% in Q2. However, AWS is much larger than both of these units, so it shouldn't surprise investors that AWS is growing at a slower rate. AWS accounted for about 18% of Amazon's total revenue in Q2, but it made up 53% of its operating profit. That's because AWS has far superior margins compared to its commerce business units, making AWS a critical part of the Amazon investment thesis.

AWS is experiencing a significant boost from AI, making it a strong stock pick in this space.

But Microsoft is also a solid AI pick, so why is Mandel moving from Microsoft to Amazon?

From a valuation perspective, both companies trade at fairly expensive levels for their growth. However, they're both priced about the same from a forward price-to-earnings (P/E) standpoint.