Based on OpenAI's structure, I would expect his equity would be in the OpenAI holding company, and not OpenAI Global, LLC which Microsoft is a minority owner of and the holding company is a majority holder. The holding company is what employees and investors have equity in.

If Altman had equity directly in OpenAI Global that would be really odd and go against OpenAIs previous disclosures.

https://openai.com/our-structure