Sam Altman has reportedly invested in more than 400 companies and has holdings worth at least $2.8 billion

• Sam Altman has invested in more than 400 companies, The Wall Street Journal reported. 
• Some firms reportedly backed by Altman do business with OpenAI, raising questions about conflicts.
• OpenAI says the company carefully manages any potential conflicts. 

Sam Altman and his venture funds have reportedly invested in more than 400 companies.

The Wall Street Journal reported that Altman is one of Silicon Valley's most prolific individual investors, with holdings worth at least $2.8 billion as of early this year.