Warren Buffett's Successor, Greg Abel, Just Sold Over 50% of Berkshire Hathaway's Stake in Nucor and Piled Into an Artificial Intelligence (AI) Stock That Billionaire Investor Bill Ackman Just Exited

Berkshire Hathaway (NYSE: BRKA) (NYSE: BRKB) recently filed its latest Form 13F with the Securities and Exchange Commission, detailing what its equity holdings were at the end of the second quarter.

Investors are always curious about what Berkshire has been buying and selling because its former chief, Warren Buffett, is widely considered one of the greatest investors of all time.

Now that he has stepped down as CEO, however, the market is even more focused on his handpicked successor, Greg Abel, who has been CEO of Berkshire since the start of the year and has already begun making some big changes at the company.

In Q2, Abel sold over 50% of Berkshire's stake in Nucor (NYSE: NUE) and piled into another artificial intelligence (AI) stock -- one that billionaire investor Bill Ackman just exited.

Warren Buffett: Image source: The Motley Fool.

Nucor: In and out

One of Buffett's core investing philosophies is that Berkshire should buy stocks it can hold forever. But it's a high threshold to meet that bar, and often, companies don't.

That appears to be the case for Nucor, the largest U.S. steelmaker. Berkshire purchased around 5.75 million shares of it at the beginning of 2025 and has since sold more than two-thirds of that initial investment over the past two quarters, including over half of its position in Q2.

The stock has performed well, including a nearly 62% gain so far in 2026 and a roughly 82% gain over the past 12 months. Nucor has been swept into the AI trade due to increasing demand for steel from the companies that are building data centers.

In Q2, Nucor's earnings before income taxes and noncontrolling interests surged by about 48% from the prior quarter, driven by strong growth across its operations. The company's largest division, steel mills, saw strong demand and higher prices.

Given that, it's hard to say exactly why Abel and the investment team at Berkshire decided to cut the conglomerate's stake in Nucor. It's obviously not a core position, so Abel and his team are likely taking gains, or perhaps they think that its earnings growth is bound to slow down.

Alphabet: An interesting time to be moving into the stock

Even before the deadline for filing 13F forms arrived, we already knew Berkshire had significantly increased its position in Alphabet (NASDAQ: GOOG)(NASDAQ: GOOGL) in Q2, given the $10 billion private placement announced at the start of June. But it looks like Berkshire also purchased an additional $7 billion of shares in the open market.

Alphabet is now the third-largest position in Berkshire's portfolio, sitting only behind Apple and American Express.

Earlier this year, Buffett said during a CNBC interview that he had been the one to initiate the conglomerate's initial Alphabet position in 2025. But it has been under Abel's watch that it grew into a top-three position in Berkshire's portfolio. (However, Buffett, who remains the executive chairman of Berkshire's board of directors, could still be behind the move.)

Either way, it's an interesting time to be buying Alphabet, given that the stock hit an all-time high in May of this year and is up nearly 150% over the past five years.

Some large hedge fund managers have begun to take their gains on Alphabet, notably Bill Ackman, whose fund Pershing Square Capital Management exited its position in the tech giant over the past two quarters.

On May 16, after selling most of Pershing Square's Alphabet position in the first quarter of the year, Ackman tweeted on X:

To be clear, our sale of $GOOG was not a bet against the company. We are very bullish long term on Alphabet. But at current valuations and in light of our finite capital base, we used $GOOG as a source of funds for $MSFT.

An investment in Alphabet is a clear bet on AI at this point, and the company is planning to spend potentially north of $200 billion on AI capital expenditures this year alone. Still, the company does have many other strong tech businesses, including YouTube, Waymo, cloud, search and advertising, and a custom chip business.

It's possible that Buffett and Abel see Alphabet as a forever stock.

Buffett has long believed in buying wonderful companies at fair prices, so while Alphabet may not have as much upside over, say, the next year, which might make it unattractive to more near-term-minded hedge funds, the Berkshire team likely still believes they are getting in at a good price over the long term.

American Express is an advertising partner of Motley Fool Money. Bram Berkowitz has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Alphabet, American Express, Apple, and Berkshire Hathaway. The Motley Fool has a disclosure policy.