Yet as UnitedHealth's stock declined, Buffett's Berkshire Hathaway Inc. (BRK.B) (BRK.A) stepped in and bought 5.04 million shares, a stake valued at $1.57 billion as of June 30's close.

Reportedly, OpenAI''s current and former staffers plan to sell about USD 6 billion worth of shares to multiple investors, including SoftBank Group, Dragoneer Investment Group, and Thrive Capital.