Warren Buffett, Michael Burry, and other top investors revealed striking portfolio changes this week. Here are 4 key trades.

Warren Buffett's Berkshire Hathaway established stakes in a trio of homebuilders last quarter: Lennar, NVR, and DR Horton. The positions were worth a combined $814 million — a small bet in the context of Berkshire's roughly $350 billion stock portfolio.

Buffett's portfolio managers, Todd Combs and Ted Weschler, were likely behind the purchases given their size. Their choices suggest they're bullish on the US housing market, despite a historic lack of affordability at the moment with mortgage rates near multi-decade highs.

The famed investor's company also raised its stakes in Capital One and Occidental Petroleum. On the other hand, it exited its wagers on McKesson, Marsh & McLennan, and Vitesse Energy in the period.

Buffett and his team also pared their positions in Activision Blizzard, Chevron, Celanese, General Motors, and Globe Life.

Michael Burry held bearish put options on S&P 500 and Nasdaq-100 index funds with a notional value of $1.6 billion at the end of June, he revealed this week.

The investor of "The Big Short" fame may have bought the puts as hedges — an offset to his raft of purchases of energy and shipping stocks last quarter.

But they could also signal he expects a stock-market crash, given his repeated warnings about a historic bubble in asset prices and predictions of a massive sell-off.

Bill Ackman boosted his exposure to AI in the second quarter. His Pershing Square fund snapped up about 1.3 million of Alphabet's Class C shares in the period, lifting the value of its position to $1.1 billion at the end of June. It also held about $262 million worth of Alphabet's Class A shares.

Moreover, Ackman and his team added to their Hilton Worldwide and Howard Hughes stakes. On the other hand, they trimmed their bets on Canadian Pacific Railway, Chipotle, Lowe's, and Restaurant Brands. 

Alphabet is one of the key players in the AI space, as it continues to invest in its Bard chatbot and make its search engine and advertising services increasingly smart.

Several of the world's leading investors and funds piled into Nvidia stock last quarter, betting the artificial-intelligence boom would continue to galvanize demand for graphics chips.

Dan Loeb's Third Point, Soros Fund Management, and Jeremy Grantham's GMO all established stakes in Nvidia last quarter. 

Meanwhile, David Tepper's Appaloosa Management, Jim Simons' Renaissance Technologies, Paul Tudor Jones' Tudor Investment Corporation, Steve Cohen's Point72 Asset Management, Stanley Druckenmiller's Duquesne Family Office, and the investment arm of the Church of Jesus Christ of Latter-day Saints all boosted their Nvidia positions in the period.

For example, RenTech ramped up its wager by almost 600-fold, securing a stake worth nearly $800 million at the end of June. Appaloosa also grew its position by nearly 600%. As for Tudor, it quadrupled the size of its Nvidia stake, and held bullish call options on nearly 600,000 shares of the chipmaker at the quarter's close.