Among individual movers, SoundHound SOUN rallied 30% after the voice AI platform provider posted a more than 200% leap in second-quarter revenue, to a record $42.7 million. It also raised its full-year midpoint sales outlook to $169 million, up from $167 million. Its loss of 3 cents per share narrowed from the year-earlier quarter.

Apple's stock surge on Wednesday added $153 billion in market capitalization to the iPhone maker, its eighth biggest one-day gain on record. Wednesday's market-cap gain was larger than the individual market caps of the smallest 435 companies in the S&P 500 index,