OpenAI Foundation is a corporation established in Delaware. It has received it's 501(c)3 status from the IRS which means donations are deductible to the fullest extent of the law (or some such; it's been a long time since I've had to write that). The American people do not own the foundation.

As for the OpenAI that is a public benefits corporation, I know nothing about all the ins and outs of that type of corporation.