She ran Instacart, then OpenAI's consumer apps, then quit to work on her own diagnosis. Simo left OpenAI in July 2026. Fortune's exclusive interview traces the move to POTS, a condition that causes her fatigue, fainting, nausea, and headaches. She co-founded ChronicleBio to study it.
POTS patients get told their labs are normal a lot. Standard panels don't flag POTS. Diagnosis usually comes from a tilt-table test and a symptom checklist, and treatment options stay generic because doctors are working from one label covering a wide range of underlying causes.
153 terabytes came out of 3,500 vials of blood. That's more than three times the 45 terabytes OpenAI used to train GPT-3.5. ChronicleBio is feeding that data into AI models built to find patterns a standard metabolic panel was never designed to catch.
The bet is splitting one diagnosis into several. ChronicleBio groups POTS patients by what their blood shows, not by a shared checklist of symptoms, so a drug trial stops averaging results across patients whose only common trait is the same diagnostic label.
A year in, the company has data, not a cure. ChronicleBio has raised $15 million and has no clinical outcome to report yet. Simo's own diagnosis is the test case: whether biomarker grouping turns a "your labs are normal" conversation into an answer.
Told your labs are normal but you still feel off? See why a normal blood test doesn't always mean you're healthy and the difference between normal and optimal ranges.