Neither Microsoft nor OpenAI’s other backers — which include Thrive Capital and Sequoia Capital — own any conventional equity shareholding in the company. Instead, they are entitled to receive a share of its profits from a specific subsidiary of OpenAI, up to a certain limit.
“While details of our agreement remain confidential, it is important to note that Microsoft does not own any portion of OpenAI and is simply entitled to share of profit distributions."
https://www.ft.com/content/458b162d-c97a-4464-8afc-72d65afb28ed