Check out the companies making the biggest moves midday: Nvidia — The chipmaker jumped 6% following the announcement it will sell more than 18,000 of its artificial intelligence chips to Saudi Arabian company Humain to be used in the latter's 500 megawatt data center. UnitedHealth Group — The insurance stock tumbled 16% to trade at lows not seen since February 2021. The sell-off came after the company said CEO Andrew Witty is stepping down for "personal reasons." The company also pulled its 2025 guidance partly due to higher medical costs, which dragged down other insurance stocks. Coinbase — Shares rallied 22% after S & P Dow Jones Indices announced that the crypto exchange operator will be added to the benchmark S & P 500 stock index before trading begins on May 19, replacing Discover Financial Services . Boeing — Shares of the aircraft company jumped 3%. Bloomberg reported Tuesday that China has lifted its ban on Boeing deliveries, citing people familiar with the matter. The company also announced it delivered 45 commercial jets in April, which is nearly twice the 24 airplanes the company delivered during the same month a year ago. On Holding — U.S.-listed shares of the Swiss-based maker of Hoka sneakers rose 12% after the company posted an earnings and revenue beat. First Solar — The solar stock soared 22%. Wolfe Research upgraded First Solar to outperform from peer perform, citing better clarity on the 45X tax credits for clean energy production. The firm said First Solar stands to earn $10 billion from the tax credit. Hertz Global Holdings — The rental car stock tumbled 15% after first-quarter results were worse than analyst expectated. Hertz reported an adjusted loss of $1.12 per share on $1.81 billion of revenue. Analysts surveyed by LSEG expected a loss of 97 cents per share and $2 billion of revenue. Revenue fell from $2.1 billion a year ago. Rigetti Computing — The quantum computing stock dropped nearly 11% after the firm posted first-quarter revenue of $1.5 million, far below the $2.6 million that analysts polled by FactSet were expecting. Earnings, however, came in better than expected for the quarter. Intuitive Machines — The Houston-based space startup soared almost 25% after its first-quarter operating income came in better than expected. While its revenue missed estimates, its free cash flow topped expectations. Caterpillar — Shares of the construction equipment giant popped almost 4% after being upgraded by Baird to outperform from neutral. The firm said the easing of tariffs is likely to drive multiple expansion for Caterpillar. Valero Energy — The stock gained 4% following an upgrade at Goldman Sachs to buy from neutral. Goldman said the oil refiner can benefit from more attractive supply-and-demand trends. Calumet — The maker of specialty products such as oils and solvents popped about 5% on the back of Bank of America's initiation at a buy rating. The bank said Calumet shares can see notable upside through growth in its biofuels business. Sea Limited — Shares added 8% after the consumer internet company reported adjusted EBITDA of $946.5 million for its first quarter, beating the $710.9 million consensus estimate, per FactSet. Revenue, however, missed expectations. —CNBC's Alex Harring, Yun Li, Tanaya Macheel, Sean Conlon and Pia Singh contributed reporting.