The Instacart CEO told Fortune the U.S. healthcare system is not well-suited to treat rare and complex diseases, which is a major opportunity for AI.

The woman behind Instacart’s successful IPO, Fidji Simo, is joining OpenAI’s C-suite. On Wednesday, OpenAI CEO Sam Altman announced Simo’s new role as CEO of Applications. She will report directly to him after transitioning out of her current role at Instacart later this year.

Simo, already a board member at OpenAI, will transition out of Instacart over the next few months and join the AI company full-time as Application CEO.