Zachary Ziegler goes by Zack. He was a PhD student in machine learning at Harvard University, where he worked with Professor Alexander Rush. He received a National Science Foundation Graduate Research Fellowship.
He co-founded OpenEvidence with Daniel Nadler, a Harvard PhD and the founder of Kensho. Ziegler is the chief technology officer. Nadler is chief executive.
OpenEvidence builds medical search and clinical decision support for doctors. By July 2025 it had 430,000 registered US physicians, about 40 percent of the total. In January 2026 it raised $250M at a $12B valuation, and in September 2026 it raised $250M at $15B.
Forbes reported that Ziegler, then 30, owned roughly 10 percent of the company. OpenEvidence lists him as a Harvard PhD candidate on its team page.