The S&P 500 notched its best first-quarter performance in five years, per CNBC.

• The index is up 10.2% so far.

Why it matters: AI euphoria, led by gains in Nvidia (up 82.5% in Q1) and expectations of rate cuts (and a soft landing), has boosted market optimism.

What we're watching: The Magnificent Seven — Apple, Amazon, Alphabet, Microsoft, Meta, Nvidia and Tesla — drove about 40% of the S&P 500's gains so far this year.

• But some are pulling away from the pack.
• Notably, Apple (down 7.6%) and Tesla (down 29.2%) have stumbled on weakening demand worries for their core products.