First interview will be a phone screen where they ask standard behavioral/fit questions: tell me about yourself and your resume, what you know about Carta, what you know about the valuations team specifically, etc. If you pass the phone screen, they'll send you a tech challenge, which is a half-built financial model that they'll ask you to complete. You'll then come on-site for 3 back-to-back 30-minute interviews--the first will be a technical interview where you'll walk through the financial model, and the next two will be behavioral/fit interviews. I heard back about 5 days after my interview and accepted the offer.
Technical interview mostly focused on technical aspects of financial modeling and DCF. I wasn't asked any questions about Black Scholes option pricing, but I'd highly recommend studying up and getting familiar with this, as it's a big part of the job.