Where can I buy OpenAI stock?

Excuse me, I'm interested in investing in OpenAI, but I'm having trouble finding out where I can purchase their stock. Could you please clarify if OpenAI is currently publicly traded, and if so, which exchange or platform would be the best place to buy their shares? Additionally, if they're not publicly traded, could you suggest any alternative ways to invest in or support the company's growth and development? Thank you for your time and assistance.