Warren Buffett's mentor, Ben Graham, wrote The Intelligent Investor, one of the most revered investment books of all time. The title of that book is an apt description of Buffett himself.

Today, though, we could perhaps describe Buffett in another way -- the artificial intelligence (AI) investor. The Oracle of Omaha ranks as one of the world's biggest investors in AI. Buffett has bet over $156 billion on two top AI stocks.

Buffett's big AI bets

It's probably not hard to guess which stock represents Buffett's biggest bet on AI. Berkshire Hathaway (BRK.A -0.56%) (BRK.B 0.07%) owns nearly $155.5 billion worth of Apple (AAPL 5.98%) stock, including shares in Berkshire subsidiary New England Asset Management's portfolio. Berkshire also has a significant stake in Amazon (AMZN 0.81%) that's currently worth more than $1.1 billion.

Together, Apple and Amazon reflect an investment of well over $156 billion. Technically, though, Buffett is even more heavily invested in AI since many of the companies in Berkshire's portfolio use the technology in their operations. However, Apple and Amazon especially stand out because of their leadership in AI. 

Apple might almost seem like an afterthought in the AI conversation in light of recent developments. But the company is clearly thinking a lot about AI. CEO Tim Cook said in Apple's first-quarter conference call in February that AI "will affect every product and every service that we have." 

Amazon, on the other hand, has made some waves in the AI world lately. Last month, the company dropped a bombshell in the AI race with the launch of Bedrock. This new AI service enables customers to quickly build and scale generative AI apps using foundational models (FMs), which are superlarge models pre-trained on massive amounts of data. Bedrock supports FMs from Amazon itself, AI21 Labs, Anthropic, and Stability AI.

Two wrinkles

One wrinkle associated with Buffett's big bet on these AI stocks is that he probably wasn't thinking about AI when Berkshire bought them. Apple has been in Berkshire's portfolio since 2016, while Amazon has been one of the conglomerate's holdings since 2019.

Sure, both Apple and Amazon were already working heavily on AI back then. However, it's fair to say that AI wasn't nearly the hot topic that it is today. Also, Buffett only invests in what he understands. He acknowledged in a CNBC interview last month that he doesn't understand AI and said that he doesn't "know if it's beneficial." 

There's another wrinkle with Amazon. Buffett didn't make the call to buy the stock. He told CNBC in 2019 that "one of the fellows in the office that manage money" -- a reference to Berkshire's investment managers Todd Combs and Ted Weschler -- initiated the purchase in the e-commerce and cloud giant. 

Still, though, Buffett really likes Amazon, saying that he was "an idiot" for not buying the stock sooner. And he absolutely loves Apple. It's by far the biggest holding in Berkshire's portfolio.

Smart bets for other investors?

Apple has taken some knocks about its lack of a clear generative AI strategy on the heels of ChatGPT's success. However, I believe the company will be a big winner in delivering AI on its devices. Apple is also reportedly working on an AI-powered health-coaching service. My hunch is that the tech giant has more AI cards to play that we don't know about yet.

Amazon's greatest opportunity in AI is with its Amazon Web Services (AWS) cloud unit. CEO Andy Jassy said in the company's recent Q1 call that "few folks appreciate how much new cloud business will happen over the next several years from the pending deluge of machine learning that's coming." 

I think that Buffett's top-two AI stocks are smart bets for other investors, too. And Apple and Amazon's AI opportunities are key reasons why I'm bullish.