Fidji Simo built her career on stamina, running Facebook's app business and then Instacart. On Thursday she told OpenAI that stamina wasn't enough this time.
Simo, who joined OpenAI in May 2025 as CEO of Applications after five years running Instacart, announced on X that she will step down from full-time leadership and move into a part-time advisory role. "Three months ago, I had to go on medical leave after a severe exacerbation of a chronic illness I've lived with for seven years," she wrote, according to CNBC. "During that time, it became clear that the road to recovery would be much longer and more complex than I had anticipated, and that I needed to focus on it fully."
The illness is postural orthostatic tachycardia syndrome, or POTS, a condition that disrupts the body's ability to regulate blood pressure and can trigger dizziness, chest pain and severe fatigue. Simo was diagnosed in 2019 and, as Fortune reported in April, saw more than 40 specialists trying to understand it before she ever mentioned it publicly. She went on leave in April after what she described internally as a particularly rough stretch health-wise, expecting to be out for a few weeks. Three months later, she isn't coming back to the job full time.
Greg Brockman, OpenAI's president, took over Simo's product responsibilities when she first went on leave. He will keep them. That detail matters more than it looks. Simo's job covered nearly everything that isn't research at OpenAI: product, engineering delivery, sales, marketing, communications, policy and legal, all rolled into one seat reporting to Sam Altman. Handing that scope to Brockman on a temporary basis is one thing. Making it permanent, even informally, tells you OpenAI didn't have a bench ready to replace her.
Simo wasn't a research pick. She was brought in specifically to professionalize a company that had grown from a research lab into a product business generating serious revenue almost overnight. Before OpenAI, she'd run Instacart through its 2023 IPO and spent nine years at Facebook building out the News Feed and then the entire app. That's the resume you hire when ChatGPT has hundreds of millions of weekly users and the company behind it is fielding IPO speculation while pushing GPT-5.6 out to the public. Her departure doesn't just remove an executive. It removes the person OpenAI recruited to prove it could run like a mature company and not just a lab racing toward a breakthrough.
OpenAI hasn't named a permanent replacement, and Brockman already carries the title of president on top of newly inherited product duties. That's a lot of surface area for one person, and it raises the obvious question of succession planning at a company that has already been through a boardroom upheaval once.
The cost the industry doesn't talk about #
Altman himself has described the environment inside OpenAI in blunt terms. "It has been an extremely intense, chaotic, and high-pressure few years," he wrote in recent reflections on the company's trajectory. "A lot of people have worked unbelievably hard to discover how to build something that most experts thought was impossible on this timeframe." That's not a confession of wrongdoing. It's a description of the pace the entire AI industry has set for itself, and Simo's exit is the clearest evidence yet that the pace has a human cost even at the very top of the org chart.
Executives don't usually explain their health in public the way Simo has. She didn't have to disclose POTS, the specialists, or the timeline. She chose to, and Fortune framed her leave in April as a rare, candid look at one of tech's most expansive jobs and what it demands of the person holding it. Whether that candor changes how the rest of the industry talks about founder and executive burnout is an open question. What's certain is that OpenAI now has to run its commercial engine, ChatGPT's growth, the enterprise pipeline, the policy fights, without the executive it hired eighteen months ago specifically to hold all of it together.
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