Greg Brockman takes charge at OpenAI as Fidji Simo steps down due to illness

Key points

• Fidji Simo, OpenAI's product and business chief, stepped down on 8 May 2026 due to a chronic illness called POTS and will become a part-time advisor.
• Greg Brockman, an OpenAI co-founder and president, will now oversee ChatGPT, enterprise sales, go-to-market teams and computing efforts.
• OpenAI confidentially filed its IPO prospectus (the formal paperwork required before a company sells shares to the public) with regulators in June 2026.
• The company carries a reported valuation of $852 billion.
• ChatGPT's share of the AI assistant market fell below 50 percent for the first time in March 2026, according to data firm Sensor Tower.

OpenAI just lost one of its most senior executives and handed her responsibilities to one of its founding members, all while quietly preparing to go public.

Fidji Simo, the company's product and business chief, stepped down on Thursday. She cited postural orthostatic tachycardia syndrome, or POTS, a condition affecting the nervous system and heart rate that can cause severe fatigue and dizziness. Diagnosed with POTS in 2019, Simo took medical leave in April 2026 and will move to a part-time advisory role.

Greg Brockman steps directly into her shoes. He co-founded OpenAI alongside CEO Sam Altman in 2015 and has been covering Simo's duties since her leave began. He now formally takes ownership of ChatGPT product, OpenAI's go-to-market and enterprise operations, and its computing strategy, reporting directly to Altman. OpenAI won't hire a replacement for Simo.

The reshuffle lands at a delicate moment. The company secretly filed its prospectus with US regulators in June 2026, though no listing date has been named and the debut is reportedly being pushed to 2027. When a company goes public, everyday investors can buy shares for the first time, and every corner of its business gets examined closely.

Brockman faces real pressure on that front. ChatGPT held below 50 percent of the AI assistant market in March 2026, per Sensor Tower. Rivals including Anthropic and Google, along with cheaper open-weight models (AI systems whose underlying code anyone can download and run), are eating into that lead. Our earlier story on OpenAI's push to put ChatGPT into family life shows how far the company is already stretching to hold users.

The Brockman-Altman partnership has its own history. When OpenAI's board briefly fired Altman in 2023, Brockman quit the same day in protest. Both returned within days. "Greg and I are partners in running this company," Altman wrote at the time.

Brockman was also in federal court in Oakland in May 2026, testifying in the lawsuit Elon Musk brought against OpenAI and its leadership. Musk alleged the company betrayed its original nonprofit mission. An advisory jury found he'd waited too long to file the case, a finding a federal judge immediately upheld. From the witness stand, Brockman said: "I think the tech we are developing is transformative."

For the millions of people who use ChatGPT at work or at home, none of this affects how the product works today. The longer question is whether Brockman can hold the company's competitive position before investors get their first look. That's not a small ask, given that the market-share slide and the Apple trade-secrets lawsuit we reported on 14 July already have the company's legal and commercial flanks under strain.

What does this mean for ordinary ChatGPT users?

Nothing changes today. Accounts, saved chats and subscription prices are unaffected by the leadership shift. The longer-term question is whether Brockman can keep OpenAI ahead of cheaper rivals, which could eventually shape what features the service prioritises and how it's priced. Worth watching, not worth panic.